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B Movsas

Publications and source records attributed to B Movsas.

At least 55 records · Page 3Linked to original sources
PubMed1997

Analyzing predictive models following definitive radiotherapy for prostate carcinoma.

BACKGROUND: As we approach the 21st century, clinically useful predictive models for prostate carcinoma are urgently needed to stratify patients reliably for future treatment strategies. Recently, many investigators have developed models that employ prostate specific antigen (PSA)-based constructs or groupings in an attempt to predict outcome accurately following definitive radiotherapy. This investigation was conducted to determine which of these models provides the closest "fit" to independent clinical outcome data measuring biochemical freedom from failure (bNED control), thereby warranting further exploration. METHODS: Six models were analyzed in a definitive radiotherapy series of 421 patients with localized prostate carcinoma treated with a median dose of 74 Gray (Gy) between March 1988 and November 1994. A stepwise Cox proportional hazards multivariate analysis (MVA) was performed to predict for bNED control using the following covariates: PSA, Gleason's score, stage, dose, PSA density, and perineural invasion. Subsequent MVAs were performed for each model incorporating the new construct or prognostic groupings. The adequacy of the models was confirmed using plots of score residuals against time to bNED failure and comparisons were made used Akaike's Information Criteria (AIC) in which a smaller value corresponds to a statistically improved model based on explained variation and the number of predictors. Because PSA was distributed in a log-normal fashion in the current study population, the model-building process was duplicated using a logarithmic transformation analysis. Biochemical failure was defined as 2 consecutive elevations in the PSA > or = 1.5 ng/mL. The median follow-up time was 34 months (range, 2-87 months). RESULTS: Initially, the model developed by Pisansky et al. appeared the most predictive due to the parsimony in their risk estimate, which is the sole predictor of outcome, as well as its associated lowest AIC value. However, after the logarithmic transformation analysis, all the models appeared to be equally predictive of bNED outcome. CONCLUSIONS: A plethora of accurate models for predicting outcome following definitive radiotherapy for prostate carcinoma recently have been engineered, all of which are essentially equally predictive in this data base (via a logarithmic conversion process). This analysis should be corroborated in other large radiotherapy series.

Follow-Up Studies↗
PubMed1997

Efficacy of a belly board device with CT-simulation in reducing small bowel volume within pelvic irradiation fields.

PURPOSE/OBJECTIVE: Acute and chronic small bowel toxicity associated with pelvic irradiation limits dose escalation for both chemotherapy and radiotherapy for rectal cancer. Various surgical and technical maneuvers including compression and belly board devices (BBD) have been used to reduce small bowel volume in treatment fields. However, quantitative dose volume advantages of such methods have not been reported. In this study, the efficacy of BBD with CT-simulation is presented with dose-volume histogram (DVH) analyses for rectal cancer. METHODS AND MATERIALS: Twelve consecutive patients referred to our department with rectal cancer were included in this study. Patients were given oral contrast 1.5 h prior to scanning and instructed not to empty their bladder during the procedure. The initial CT scan without BBD was taken in the prone position with an immobilization cast. A second CT study was performed with a commercially available BBD consisting of an 18-cm thick hard sponge with an adjustable opening (maximum 42 x 42 cm2). All patients were positioned prone over the BBD so that the opening was above the treatment volume and usually extended from the diaphragm to the bottom of the fourth lumbar spine. Image fusion between both sets of CT scans (with and without BBD) was performed using common bony landmarks to maintain the same target volume. The critical structures including small bowel and bladder were delineated on each slice for DVH analysis. On each study, a three-field optimized plan with conformal blocks in beams-eye-view was generated for volumetric analysis. The DVHs with and without BBD were evaluated for each patient. RESULTS: The median age and body weight of 12 patients (4 females and 8 males) were 57.5 years and 82.7 kg, respectively. The changes in posterior-anterior (PA) and lateral separation with and without BBD at central axis slices were analyzed. The changes in lateral separation were minimal (<0.8 cm); however, the PA separation was reduced by 11.3 +/- 3.3% when BBD was used. The reduction in PA separation was directly related to the reduction in small bowel volume. The small bowel volume was significantly reduced with a median reduction of 70% (range 10-100%) compared to the small bowel volume without BBD. The small bowel volume reduction did not correlate either with body weight, age, gender, or sequence of radiation treatment with surgery (pre-op vs. post-op). The DVH analysis of small bowel with BBD showed significant volume reduction at each dose level. For 50% patients, the DVH analysis demonstrated an increase in bladder volume with BBD. All patients treated with the BBD completed their treatment without any break and without significant acute gastrointestinal or genitourinary toxicity. CONCLUSIONS: For rectal cancers, small bowel is the dose-limiting structure for acute and chronic toxicity. The use of the BBD should improve the tolerance of aggressive combined modality treatment by reducing the small bowel volume within the pelvis compared to the prone position alone. The BBD provides an easy, economical, comfortable, and noninvasive technique to displace small bowel from pelvic treatment fields. The small bowel volume is dramatically reduced at each dose level. The volume reduction does not correlate with gender, age, weight, pelvic separation, and sequence of radiation treatment vs. surgery.

Aged↗
PubMed1997

Chronic rectal bleeding after high-dose conformal treatment of prostate cancer warrants modification of existing morbidity scales.

PURPOSE: Serious late morbidity (Grade 3/4) from the conformal treatment of prostate cancer has been reported in <1% to 6% of patients based on existing late gastrointestinal (GI) morbidity scales. None of the existing morbidity scales include our most frequently observed late GI complication, which is chronic rectal bleeding requiring multiple fulgerations. This communication documents the frequency of rectal bleeding requiring multiple fulgerations and illustrates the variation in reported late serious GI complication rates by the selection of morbidity scale. METHODS AND MATERIALS: Between May 1989 and December 1993, 352 patients with T1-T3 nonmetastatic prostate cancers were treated with our four-field conformal technique without special rectal blocking. This technique includes a 1-cm margin from the clinical target volume (CTV) to the planning target volume (PTV) in all directions. The median follow-up for these patients was 36 months (range 2-76), and the median center of prostate dose was 74 Gy (range 63-81). Three morbidity scales are assessed: the Radiation Therapy Oncology Group (RTOG), the Late Effects Normal Tissue Task Force (LENT), and our modification of the LENT (FC-LENT). This modification registers chronic rectal bleeding requiring at least one blood transfusion and/or more than two coagulations as a Grade 3 event. Estimates for Grade 3/4 late GI complication rates were determined using Kaplan-Meier methodology. The duration of severe symptoms with chronic rectal bleeding is measured from the first to the last transrectal coagulation. Latency is measured from the end of radiotherapy to surgery, first blood transfusion, or third coagulation procedure. RESULTS: Sixteen patients developed Grade 3/4 complications by one of the three morbidity scales. Two patients required surgery (colostomy or sigmoid resection), three required multiple blood transfusions, two required one or two blood transfusions, and nine required at least three coagulations. The median duration of bleeding for those patients requiring multiple procedures was 7 months (range 3-33) and the median latency was 22 months (range 9-40). The 5-year actuarial rate of Grade 3/4 complications by each scale are: RTOG 0.7%, LENT 2%, and FC-LENT 6%. The rate of chronic rectal bleeding increases with increasing dose and is low in patients treated with conventional techniques owing to lower doses. CONCLUSION: Chronic rectal bleeding requiring any blood transfusion(s) or multiple coagulation procedures is our most frequently observed complication. This complication appears late in follow-up and is present for a long duration. We believe this justifies the inclusion of chronic rectal bleeding requiring multiple coagulation procedures as a Grade 3 event in future morbidity scales. Our data illustrate that published Grade 3/4 morbidity rates are highly dependent on the morbidity scale selected, as our data show 0.7% RTOG, 2% LENT, and 6% FC-LENT. Obviously, a uniform scale is required that includes the newly recognized serious late effects associated with the conformal treatment of prostate cancer.

Aged↗
PubMed1997

Evidence of increased failure in the treatment of prostate carcinoma patients who have perineural invasion treated with three-dimensional conformal radiation therapy.

BACKGROUND: The detection of perineural invasion (PNI) in the diagnostic transrectal biopsy of the prostate is associated with a 93% frequency of extracapsular disease extension in patients treated by prostatectomy for adenocarcinoma of the prostate. Extracapsular extension is associated with an inferior outcome compared with that of patients who have organ-confined disease. This study examined the association of PNI and treatment failure in a consecutive series of patients treated with three-dimensional conformal radiation therapy (3DCRT) alone. METHODS: The authors report actuarial biochemical no evidence of disease (bNED) survival rates for 484 consecutive patients with clinically localized prostate carcinoma diagnosed by transrectal needle biopsy who completed 3DCRT alone between May 1989 and December 1994. The median follow-up time was 28 months (range, 2-75 months), and the median dose to the center of the prostate was 7368 centigray (cGy) (range, 6316-8074 cGy). Patients were subdivided into 2 groups according to pretreatment prostate specific antigen (PSA) levels (< 20 ng/mL vs. > or = 20 ng/mL). Pathology records were reviewed for the presence or absence of PNI. bNED failure was defined as a PSA level > or = 1.5 ng/mL and rising on 2 consecutive occasions. bNED survival rates were calculated using Kaplan-Meier methodology and comparisons of survival curves were accomplished using the log rank test. RESULTS: The 3-year bNED survival for all 484 patients was 77%. The presence of PNI predicted decreased bNED survival in all patients. This detrimental effect, however, was confined to patients with pretreatment PSA values < 20 ng/mL. The bNED survival rates for patients with pretreatment PSA < 20 ng/mL demonstrated a highly significant decrease if PNI was present versus when it was absent (65% vs. 88% at 3 years, 39% vs. 65% at 5 years; P = 0.0009 for overall curve comparison). For patients with pretreatment PSA < 20 ng/mL, multivariate analysis of prognostic variables demonstrated a significant association between bNED survival and PNI (P = 0.002), palpation stage (P = 0.02), and pretreatment PSA (P = 0.006). Gleason score, age, and dose were not independent predictors of bNED survival in this group of patients. CONCLUSIONS: To the authors' knowledge, this is the first report demonstrating that PNI detected on diagnostic transrectal biopsy is a significant predictor of decreased bNED survival in patients treated with radiotherapy. The subgroup of patients affected are those with pretreatment PSA < 20 ng/mL. This result suggests that such patients may benefit from more aggressive treatment, particularly the use of larger planning target volumes or adjuvant therapies.

Aged↗
PubMed1997

Postradiotherapy PSA nadirs fail to support dose escalation study in patients with pretreatment PSA values < 10 ng/ml.

With three-dimensional conformal therapy, doses > 75 Gy have been delivered to the prostate with acceptable levels of morbidity; however, higher doses do appear to increase late gastrointestinal (GI) and genitourinary (GU) morbidity. Because patients with pretreatment prostate-specific antigen (PSA) values < 10 ng/ml can achieve 3-year actuarial bNED control rates of 90% after treatment with external beam radiotherapy to doses < 71 Gy, one might question the need for further dose escalation in this population. In this report, we examined the relationship between dose and PSA nadir for 90 patients with pretreatment PSA values < 10 ng/ml entered into a dose escalation study from March 1987 to October 1992. We wanted to see if nadir response data would predict a different outcome from our 3-year bNED control reports. All patients were treated with external beam radiotherapy to ICRU reporting point doses of 6,598 cGy to 7,895 cGy (median of 7,068 cGy). Minimum follow-up was 36 months (median, 47 months). Seven hundred thirty-nine posttreatment PSA nadir values were analyzed, yielding an average of 8.2 values per patient. Estimates of rates of bNED control and time to reach a posttreatment PSA of 1.0 ng/ml were calculated using the Kaplan-Meier product limit method. The log-rank test was used to evaluate differences in rates according to dose levels. Linear regression and Cox proportional hazard modeling were used to relate dose to bNED control on a continuum. Escalating doses from 66 to 79 Gy failed to increase the percentage of patients achieving nadir values < 1 ng/ml and similarly failed to increase the 3-year actuarial bNED control. Linear regression (P = .81) and the chi-square test of association (P = .23) supported the lack of a dose effect on nadir continuously and categorically, respectively, and the Cox regression model supported the conclusion that dose on a continuum has no effect on bNED control (P = .34). Furthermore, time to reach a posttreatment PSA level of 1.0 ng/ml was not statistically dependent on dose level (P = .13). Based on this study and prior reports demonstrating a dose response for late GI/GU morbidity, we question whether further dose escalation in this subgroup of patients is justified.

Biomarkers, Tumor↗
PubMed1997

Computed tomography-magnetic resonance image fusion: a clinical evaluation of an innovative approach for improved tumor localization in primary central nervous system lesions.

We describe our initial experience with the AcQSim (Picker International, St. David, PA) computed tomography-magnetic resonance imaging (CT-MRI) fusion software in eight patients with intracranial lesions. MRI data are electronically integrated into the CT-based treatment planning system. Since MRI is superior to CT in identifying intracranial abnormalities, we evaluated the precision and feasibility of this new localization method. Patients initially underwent CT simulation from C2 to the most superior portion of the scalp. T2 and post-contrast T1-weighted MRI of this area was then performed. Patient positioning was duplicated utilizing a head cup and bridge of nose to forehead angle measurements. First, a gross tumor volume (GTV) was identified utilizing the CT (CT/GTV). The CT and MRI scans were subsequently fused utilizing a point pair matching method and a second GTV (CT-MRI/GTV) was contoured with the aid of both studies. The fusion process was uncomplicated and completed in a timely manner. Volumetric analysis revealed the CT-MRI/GTV to be larger than the CT/GTV in all eight cases. The mean CT-MRI/GTV was 28.7 cm3 compared to 16.7 cm3 by CT alone. This translated into a 72% increase in the radiographic tumor volume by CT-MRI. A simulated dose-volume histogram in two patients revealed that marginal portions of the lesion, as identified by CT and MRI, were not included in the high dose treatment volume as contoured with the use of CT alone. Our initial experience with the fusion software demonstrated an improvement in tumor localization with this technique. Based on these patients the use of CT alone for treatment planning purposes in central nervous system (CNS) lesions is inadequate and would result in an unacceptable rate of marginal misses. The importation of MRI data into three-dimensional treatment planning is therefore crucial to accurate tumor localization. The fusion process simplifies and improves precision of this task.

Brain Neoplasms↗
PubMed1997

Conformal external beam treatment of prostate cancer.

OBJECTIVES: This study reports the 5-year outcomes of treatment for patients with prostate cancer treated largely with conformal three-dimensional radiation therapy. METHODS: Results are presented for 456 consecutive patients treated prior to December 31, 1993 whose pretreatment prostate-specific antigen (PSA) levels are known. Biochemical failure was defined as two consecutive rises in the PSA that equals or exceeds 1.5 ng/mL. Kaplan-Meier product limit methods, the log-rank test, and Cox regression models were used in evaluating the data. No patient was lost to follow-up. RESULTS: The 5-year biochemically free of failure (bNED) rate for all patients was 61% and 57% at 7 years. In the group with pretreatment PSA less than 10 ng/mL, the 5-year bNED rate for patients with localized disease (T1,2AB disease, Gleason sum of 6 or less) was 85% and for those with locally advanced disease (T2C,3), 70%. In the group with pretreatment PSA of 10 to 19.9 ng/mL, the 5-year bNED rate for patients with localized disease was 66% and for those with locally advanced disease, 44%. In the group with pretreatment PSA of 20 ng/mL or above, the patients with localized or locally advanced disease had 5-year bNED rates of 31% and 21%, respectively. CONCLUSIONS: The results of largely conformal three-dimensional external beam treatment of localized prostate cancer produced 5-year bNED results that are comparable to recent reports of nerve-sparing prostatectomy. Preliminary 7-year bNED results in all patients and in patients with localized tumors indicated a modest decrease in the cancer-free rate from that observed at 5 years, suggesting the results are durable.

Humans↗
PubMed1997

Induction paclitaxel and carboplatin followed by concurrent chemoradiotherapy in patients with unresectable, locally advanced non-small cell lung carcinoma: report of Fox Chase Cancer Center study 94-001.

The paclitaxel (Taxol; Bristol-Myers Squibb Company, Princeton, NJ)/carboplatin combination has demonstrated promising activity in patients with incurable non-small cell lung cancer (NSCLC). Our exploratory study is designed to evaluate the efficacy of this combination as induction therapy in patients with locally advanced NSCLC, to determine the maximally tolerated doses of paclitaxel and carboplatin administered every 3 weeks during radical thoracic radiation after induction treatment, and to determine the efficacy of granulocyte colony-stimulating factor (G-CSF) priming before induction treatment, followed by conventional G-CSF, compared with conventional G-CSF alone. Eligibility stipulated Karnofsky performance status > or =70%, < or =5% weight loss, and stages IIIB or bulky IIIA NSCLC. Induction treatment consisted of two cycles of paclitaxel 175 to 225 mg/m2 infused over 3 hours combined with carboplatin (target area under the concentration-time curve of 7.5) given on days 1 and 22. On days 2 through 15 and 23 through 36, all patients received G-CSF 5 microg/kg; half were randomized to receive priming G-CSF daily for 5 days before day 1 of treatment. On day 43, thoracic radiation (60 Gy in 30 2-Gy fractions daily, 5 days a week for 6 weeks) was initiated. At dose level 1, patients received carboplatin dosed to a target area under the concentration-time curve of 3.75 and paclitaxel 67.5 mg/m2 over 3 hours on days 43 and 64. In the absence of dose-limiting toxicity, phase I escalation in three-patient cohorts proceeded to a maximum carboplatin area under the concentration-time curve of 5.0 and a paclitaxel dose of 175 mg/m2, delivered over 3 hours. To date, 35 patients (83% stage IIIB) have received induction treatment, 29 of whom are evaluable for response. Myelosuppression and neurotoxicity have been mild during induction treatment, prompting a paclitaxel dose increase to 225 mg/m2 on days 1 and 22 after the first seven patients were accrued. The phase III portion of the study evaluating G-CSF priming remains coded. Sixteen patients have received concurrent thoracic radiation and chemotherapy and are evaluable for response and toxicity. In sequential cohorts, the paclitaxel dose on days 43 and 64 has been escalated to 175 mg/m2 with only one episode each of grade 4 granulocytopenia and grade 3 anemia. In the first 13 patients evaluated, the severity of esophagitis corresponded to the length of the esophagus in the radiation treatment field: grade 1 in all six patients with esophageal exposure < or =16 cm and grade > or =2 in six of seven patients with > or =16 cm of the esophagus irradiated. Three episodes of grade > or =2 steroid-responsive pulmonary toxicity have occurred 2 to 6 months after the conclusion of concurrent thoracic radiation and chemotherapy. The major response rate is 38% to induction treatment and 59% to combined-modality treatment. Of the first 21 patients accrued, 62% survived 1 year. Induction paclitaxel/carboplatin therapy is active and well tolerated by patients with locally advanced NSCLC. The maximum tolerated doses of paclitaxel and carboplatin during concurrent thoracic radiation and the role of G-CSF priming are not yet established. Severity of esophagitis corresponds to the extent of esophagus irradiated during concurrent thoracic radiotherapy and chemotherapy.

Adult↗
PubMed1996

Conformal technique dose escalation for prostate cancer: biochemical evidence of improved cancer control with higher doses in patients with pretreatment prostate-specific antigen > or = 10 NG/ML.

PURPOSE: Conformal radiation technology results in fewer late complications and allows testing of the value of higher doses in prostate cancer. METHODS AND MATERIALS: We report the biochemical freedom from disease (bNED) rates (bNED failure is Prostate Specific Antigen (PSA) > or = 1.5 ng/ml and rising) at 2 and 3 years for 375 consecutive patients treated with conformal technique from 66 to 79 Gy. Median follow-up was 21 months. Biochemical freedom from disease was analyzed for patients treated above and below 71 Gy as well as above and below 73 Gy. Each dose group was subdivided by pretreatment PSA level (< 10, 10-19.9, and > or = 20 ng/ml). Dose was stated to be at the center of the prostate gland. RESULTS: There was significant improvement in bNED survival for all patients divided by a dose above or below 71 Gy (p = 0.007) and a marginal improvement above or below 73 Gy (p = 0.07). Subdividing by pretreatment PSA level showed no benefit to the PSA < 10 ng/ml group at the higher dose but there was a significant improvement at 71 and 73 Gy for pretreatment PSA 10-19.9 ng/ml (p = 0.03 and 0.05, respectively) and for pretreatment PSA > or = 20 ng/ml (p = 0.003 and 0.02, respectively). CONCLUSIONS: Increasing dose above 71 or 73 Gy did not result in improved bNED survival for patients with pretreatment PSA < 10 ng/ml at 2 or 3 years. Further dose escalation studies may not be useful in these patients. A significant improvement in bNED survival was noted for patients with pretreatment PSA > or = 10 ng/ml treated above 71 or 73 Gy; further dose escalation studies are warranted.

Aged↗
PubMed1995

Long-term visual changes following pituitary irradiation.

PURPOSE: To analyze possible long-term effects of pituitary irradiation on visual fields and acuity. METHODS AND MATERIALS: Eighty-six patients were treated with radiotherapy for pituitary tumors at the National Cancer Institute between 1980 and 1991. Twenty-one patients had baseline preradiation and long-term follow-up visual fields. Eyes were followed with serial Goldmann or Humphrey visual field testing. Neuroradiologic correlation was made with the available brain scans. There were 12 females and 9 males with an median age of 44. Eighteen patients had hormone-secreting tumors and three had chromophobe adenomas. All but one patient with an inoperable invasive macroadenoma were irradiated after one or more transphenoidal resections or a craniotomy. The indications for radiation in the operable patients were: nine patients, partial tumor resection; nine patients, tumor recurrence; and two patients, persistent hormonal elevation after surgery. The median dose delivered was 50 Gy (45-59.4 Gy). The average field size was 6 x 6 cm (5 x 5 cm to 10 x 12.5 cm). RESULTS: With a median follow-up of 48 months (14-128) after radiotherapy, 1 out of 21 patients has recurred (at 8 months) and all patients are alive. Of the 38 sighted eyes, 27 had normal visual fields before and after radiation, 7 eyes showed improvement, and 4 eyes had a stable defect, mostly in the superior temporal region. There were no cases of radiation-induced visual field or acuity deterioration. Six out of 21 patients (29%) had neurologic symptoms in follow-up, most of which appeared vascular in nature. Four patients complained of atypical migranous-like headaches that first began 1.5-3 years following treatment. One patient complained of recurrent vertical diplopia and one patient had a cerebral vascular accident 7 years following therapy. A dose-related association with these neurovascular symptoms approached statistical significance. Only 1 out of 11 (9%) patients who received doses less than or equal to 50 Gy developed these symptoms, whereas 5 out of 10 (50%) patients who received doses greater than 50 Gy developed symptoms (p2 = 0.064). CONCLUSION: Postoperative radiation for partially resected or recurrent pituitary adenomas using megavoltage radiation, as well as modern field arrangements and fractionation, is extremely effective and safe. Ninety-five percent of patients are free of recurrence with not deterioration in the visual fields or acuities. Some patients experienced neurovascular symptoms (mostly vascular headaches) following surgery and radiation. There is a trend (p2 = 0.064) toward increased symptoms following higher radiation doses.

Adenoma↗
PubMed1995

Response of non-Hodgkin lymphoma to radiation therapy: early and long-term assessment with H-1 MR spectroscopic imaging.

PURPOSE: To determine whether proton magnetic resonance (MR) spectroscopic imaging is a sensitive technique for defining tumor extent and assessing response of cerebral lymphoma to therapy. MATERIALS AND METHODS: Four hydrogen-1 MR spectroscopic imaging studies were performed in a patient with non-Hodgkin lymphoma (NHL) before, during, and after radiation therapy and at follow-up at 33 months after diagnosis of the recurrence of disease. The patient had a single, large lesion in the brain and underwent hyperfractionated radiation therapy for 4 weeks. A series of MR images was also obtained. RESULTS: The pretreatment study showed a lesion with a distinct spectral pattern: marked elevation of choline and lipids and great reduction of creatine and N-acetylaspartate. During and after treatment, H-1 MR spectroscopic images depicted a progressive reduction of the abnormal choline and lipid signals. Thirty-three months after treatment, multiple-section H-1 MR spectroscopic images showed normal spectral patterns in all sections examined. CONCLUSION: H-1 MR spectroscopy may contribute to the neuroradiologic evaluation of NHL and, in particular, may be useful in monitoring therapeutic response.

Aspartic Acid↗
PubMed1989

Activation of glnA transcription by nitrogen regulator I (NRI)-phosphate in Escherichia coli: evidence for a long-range physical interaction between NRI-phosphate and RNA polymerase.

Growth of cells of Escherichia coli in nitrogen-limited medium induces the formation of glutamine synthetase, product of the glnA gene, and of other proteins that facilitate the assimilation of nitrogen-containing compounds. Transcription from the glnAp2 promoter of the glnALG operon requires the phosphorylation of nitrogen regulator I (NRI) and, for optimal transcription, the binding of NRI-phosphate to two sites that can be over 1,000 base pairs from the binding site for RNA polymerase. In other procaryotic genes, placement of an activator-binding site further upstream from the start site of transcription diminishes expression. To determine how NRI-phosphate activates transcription and why NRI-dependent transcription differs from activation in other systems, we constructed recombinant plasmids with small alterations between the binding sites for NRI-phosphate and RNA polymerase and between the two high-affinity NRI-binding sites. We demonstrate that tightly bound NRI-phosphate activated transcription from either side of the DNA helix when at least 30 base pairs separated NRI-phosphate from RNA polymerase. In contrast, activation from a partial NRI-binding site was effective only from one side of the DNA. We also observed that glnA expression was optimal when the two high-affinity NRI-binding sites were on the same side of the DNA helix. We explain these results on the basis of a hypothesis that a contact between RNA polymerase and NRI-phosphate bound to an upstream site determines the rate of glnA transcription.

Bacterial Proteins↗
PubMed1985

Degradation of the 34 amino acid gastrin by rat tissue homogenates.

Extracts of rat kidney contain an enzyme (gastrinase) that is highly specific for degradation of the 34 amino acid gastrin (G34). The Michaelis constant (Km) for kidney is 0.36 +/- 0.04 microM and the Vmax is 9.5 +/- 2.4 nmol X g-1 X min-1. Extracts of liver and brain also have gastrin degrading activity but the enzymes responsible appear to be different from the kidney gastrinase. Km for the liver enzyme is 0.08 +/- 0.02 microM but its Vmax (0.10 +/- 0.02 nmol X g-1 X min-1) is only 1% of the kidney gastrinase; Km for the brain enzyme is 0.10 +/- 0.03 microM but its Vmax (0.023 +/- 0.007 nmol X g-1 X min-1) is even lower than for the liver enzyme. The liver and brain enzymes appear to be less specific than the kidney enzyme with respect to competitive inhibition by insulin and glucagon. Cholecystokinin octapeptide is less inhibitory than the other peptides even though it shares a common C-terminal pentapeptide with G34. These findings are consistent with in vivo studies which have demonstrated that the dog kidney is an important site for extraction and degradation of endogenous dog gastrin but there is little or no hepatic removal of G34.

Animals↗
PubMed1984

Characterization of insulinase from mammalian and non-mammalian livers.

The Michaelis constants (Km's) and maximum reaction velocities (Vmax's) for the degradation of beef insulin by livers from frogs, guinea pigs, rats, a rabbit, a dog and a pig were determined. The Km's for mammalian livers appear to be species-dependent and range from 0.25 microM to 0.65 microM. The Km for frog liver was somewhat lower, averaging 0.13 microM. The Km is independent of animal age, but the enzyme concentrations (Vmax) were greatly reduced in the fetal guinea pig and 3 day rat compared to the adult livers. There appears to be no relation between Km and the chemical dissimilarity between beef insulin and endogenous insulin of the species, since guinea pig liver insulinase had a Km (0.50 microM) intermediate between dog (0.47 microM) and pig (0.65 microM) liver insulinase although guinea pig insulin has a markedly different amino acid sequence and biologic activity.

Aging↗