Search PubMed⌕ Search

Biomedical subjects

J M Becker

Publications and source records attributed to J M Becker.

At least 109 records · Page 6Linked to original sources
PubMed1992

Preservation and propagation of cyclic myoelectric activity after feeding in rat small intestine.

The cyclic nature and distal propagation of the fasting migrating motor complex (MMC) of the small intestine have been well described. The fate of the MMC after feeding, however, has not been elucidated. We used time series analysis with fast Fourier transforms (FFT) to study myoelectric cycling before and after feeding. Ten rats were chronically prepared with bipolar electrodes secured to the duodenum and proximal jejunum. Spikeburst frequency was recorded before and after feeding simple nutrients. During fasting, cyclic activity occurred at the MMC frequency. Although after feeding this periodicity appeared disrupted, FFT analysis showed persistent cycling at the fasted (MMC) rate. Digital filtering of data at the MMC frequency isolated cycling from background noise during both fasted and fed states and showed a depression in the amplitude of the waveform after feeding. Root-mean-square analysis of the waveform confirmed statistically significant depression of amplitude by 47-57%. The waveform propagated from the duodenum to the jejunum during both the fasted and fed state at an unchanged rate. We conclude that factors controlling myoelectric cycling during the fasted state persist after feeding, allowing continued net abroad propulsion of food.

Administration, Oral↗
PubMed1991

The conformation of a-factor is not influenced by the S-prenylation of Cys12.

Two-Dimensional NMR was used to examine the solution conformation of the lipopeptide a-factor, YIIKGVFWDPAC (S-farnesyl) OCH3, from the yeast Saccharomyces cerevisiae and five analogues containing various S-alkylated cysteines in DMSO-d6. NOESY data, NH temperature coefficients, and 3J alpha NH coupling constants indicate that the a-factor is a predominantly unstructured peptide in DMSO. Similar results were obtained for the other peptides indicating that S-prenylation of Cys12 does not affect the conformation of these peptides.

Acylation↗
PubMed1991

Mass spectrometric signature of S-prenylated cysteine peptides.

The fast atom bombardment mass spectra of peptides containing S-prenylated cysteine display signature fragmentations characteristic of this modified amino acid. The fragmentation is independent of the nature of the cysteine carbonyl substituent, easily differentiates prenyl from nonprenyl alkylation, and readily identifies the oligomer count of the prenyl. This screening method, which requires little time, effort, or material (compared with previous analysis methods based on chemical degradation), greatly facilitates the identification of these prenylated proteins.

Amino Acid Sequence↗
PubMed1991

Isolation and characterization of S. cerevisiae mutants deficient in amino acid-inducible peptide transport.

The transport of small peptides into the yeast Saccharomyces cerevisiae is subject to complex regulatory control. In an effort to determine the number, and to address the function, of the components involved in peptide transport and its regulation, spontaneous mutants resistant to toxic di- and tripeptides were isolated under inducing conditions. Twenty-four mutant strains were characterized in detail and fell into two phenotypic groups; one group deficient in amino acid-inducible peptide uptake, the other with a pleiotropic phenotype including a loss of peptide transport. Complementation analysis of recessive mutations in 12 of these strains defined three groups; ptr1 (nine strains), ptr2 (two strains), and ptr3 (one strain). Isolation and screening of 31 additional N-methyl-N-nitro-N-Nitrosoguanidine (MNNG)-induced, peptide transport-deficient mutants produced one ptr3 and 30 ptr2 strains: no additional complementation groups were detected. Uptake of radiolabeled dileucine was negligible in ptr1 and ptr2 strains and was reduced by 65% and 90% in the two ptr3 mutants, indicating that all strains were defective at the transport step. We conclude that the S. cerevisiae amino acid-inducible peptide transport system recognizes a broad spectrum of peptide substrates and involves at least three components. One gene, PTR3, may play an indirect or regulatory role since mutations in this gene cause a pleiotropic phenotype.

Amino Acids↗
PubMed1991

Laparoscopic cholecystectomy.

Laparoscopic cholecystectomy has emerged in the last 2 years as a unique procedure that offers the long-term advantages of open cholecystectomy without much of the short-term morbidity. Importantly, when compared with non-surgical approaches to symptomatic gallstones, it is suitable for virtually all patients rather than a highly-selected group as in the case of oral bile salt dissolution therapy or extracorporeal lithotripsy. Furthermore, it obviates the high recurrence rate seen with these techniques. Complications including bleeding and ductal injury appear to occur at a slightly higher rate than with traditional open cholecystectomy, but most surgeons who have had experience with the procedure predict that these complications will become rarer as more experience is gained. We may indeed be witnessing the first major successful challenge to traditional surgical management of symptomatic gallstone disease in 100 years.

Cholecystectomy↗
PubMed1991

Synthesis and biological evaluation of dipeptidyl and tripeptidyl polyoxin and nikkomycin analogues as anticandidal prodrugs.

Nine analogues (1-5, 9-12) of the peptidyl nucleoside antibiotics nikkomycin and polyoxin were synthesized and tested for their biological properties against different strains of the pathogenic yeast Candida albicans. The tripeptidyl series of analogues (1-5) was designed to behave as prodrugs, releasing a toxic moiety upon enzymatic hydrolysis inside the cell. The dipeptidyl series (9-12) was designed as double-targeted drugs, being themselves toxic and releasing a toxic amino acid upon hydrolysis. All the analogues were prepared by coupling suitably protected amino acid p-nitrophenyl esters to 1-(5'-amino-5'-deoxy-alpha-D-allofuranuronosyl)uracil (UPOC) or the corresponding polyoxins and nikkomycins, with subsequent removal of the protecting group. Improved coupling yields were observed when DMSO was used as the solvent. Products were purified with use of reversed-phase HPLC and, in one case, diastereomeric products (compound 11) were resolved by using this procedure. One of the tripeptidyl nikkomycins behaved as a prodrug but none of the compounds, as measured by in vitro testing, proved more effective than nikkomycin as an anticandidal agent.

Aminoglycosides↗
PubMed1991

Colectomy, mucosal proctectomy, and ileal pouch-anal anastomosis. A prospective trial of optimal antibiotic management.

The ideal prophylactic antibiotic regimen has not been established for patients undergoing colectomy, mucosal proctectomy, and endorectal ileoanal anastomosis, a prolonged operation frequently accompanied by abdominal and pelvic contamination and associated with an infection rate up to 20%. The aim of this study was to evaluate, in a prospective, randomized, double-blind fashion, the efficacy of a short perioperative course compared to an extended postoperative course of intravenous antibiotics (cefoxitin) in patients undergoing colectomy with ileoanal anastomosis. Forty patients with ulcerative colitis or familial polyposis coli received a mechanical and oral antibiotic bowel preparation and a standard three-dose perioperative course of intravenous cefoxitin. Patients then were randomized to receive intravenous cefoxitin, 1 g every 6 hours, or placebo for 5 days. No differences in overall postoperative morbidity were observed and neither group developed intra-abdominal, pelvic, or wound infections. It is concluded that a standard three-dose perioperative course of intravenous antibiotics provides adequate prophylaxis in the prevention of infectious complications in patients undergoing colectomy, mucosal proctectomy, and ileoanal anastomosis.

Adenomatous Polyposis Coli↗
PubMed1991

Synthesis of S-alkyl and C-terminal analogs of the Saccharomyces cerevisiae a-factor. Influence of temperature on the stability of Fmoc and OFm groups toward HF.

The a-mating factor of Saccharomyces cerevisiae Tyr-Ile-Ile-Lys-Gly-Val-Phe-Trp-Asp-Pro-Ala-Cys(farnesyl)OCH3, and 10 analogs modified at the cysteine side chain and/or the terminal carboxyl were synthesized using a combination of solid phase and solution phase methodologies. The strategy of synthesis involved the condensation of an amine terminal protected decapeptide with a carboxyl terminal S-alkylated dipeptide ester or amide using benzotriazol-l-yloxy-tris(methylamino)-phosphonium hexafluorophosphate as the coupling agent. The protected decapeptide was assembled on a PAM-resin using 9-fluorenylmethoxycarbonyl (Fmoc) for the protection of the Tyr alpha-amine and Lys epsilon-amine and 9-fluorenylmethyl ester (OFm) for the protection of the Asp beta-carboxyl. Premature loss of the OFm group from the HF cleavage was observed at 0-2 degrees, whereas no loss occurred when the cleavage reaction was conducted at -5 degrees. In contrast to these results, the OFm group in Asp(OFm) was partially removed by HF at -5 degrees and was completely stable to HF only at -20 degrees. The S-alkylated dipeptide esters were prepared, in yields from 64% to 88%, via thioalkylation of amine protected or unprotected dipeptide esters using potassium fluoride dihydrate as the base. The use of a tertiary amine as the base of thiohexadecanylation resulted in low reactivity.

Alkylation↗
PubMed1991

Degradation of a-factor by a Saccharomyces cerevisiae alpha-mating-type-specific endopeptidase: evidence for a role in recovery of cells from G1 arrest.

Mating response between opposite mating types of Saccharomyces cerevisiae is dependent upon alpha factor, a tridecapeptide, and a-factor, an isoprenylated, methyl esterified dodecapeptide whose interaction with the alpha target cell has not been characterized. We report on the first biochemical and physiological evidence of an alpha-mating-type-specific a-factor-degrading activity. Radioiodinated a-factor was used to identify the a-factor-degrading activity, which is cell associated, endoproteolytic, and not required for response to pheromone. a-factor degradation was not energy dependent, nor did it require pheromone internalization or interaction with its receptor. Phenylmethylsulfonyl fluoride and tosyl-L-arginyl-methyl ester inhibited degradation of a-factor and increased the time required by alpha cells to recover from a-factor-induced growth arrest and morphological alteration, providing evidence that a-factor degradation plays a role in the recovery of alpha cells from the pheromone response.

Amino Acid Sequence↗
PubMed1991

Significance of C-terminal cysteine modifications to the biological activity of the Saccharomyces cerevisiae a-factor mating pheromone.

We have undertaken total synthesis of the Saccharomyces cerevisiae a-factor (NH2-YIIKGVFWDPAC[S-farnesyl]-COOCH3) and several Cys-12 analogs to determine the significance of S-farnesylation and carboxy-terminal methyl esterification to the biological activity of this lipopeptide mating pheromone. Replacement of either the farnesyl group or the carboxy-terminal methyl ester by a hydrogen atom resulted in marked reduction but not total loss of bioactivity as measured by a variety of assays. Moreover, both the farnesyl and methyl ester groups could be replaced by other substituents to produce biologically active analogs. The bioactivity of a-factor decreased as the number of prenyl units on the cysteine sulfur decreased from three to one, and an a-factor analog having the S-farnesyl group replaced by an S-hexadecanyl group was more active than an S-methyl a-factor analog. Thus, with two types of modifications, a-factor activity increased as the S-alkyl group became bulkier and more hydrophobic. MATa cells having deletions of the a-factor structural genes (mfal1 mfa2 mutants) were capable of mating with either sst2 or wild-type MAT alpha cells in the presence of exogenous a-factor, indicating that it is not absolutely essential for MATa cells to actively produce a-factor in order to mate. Various a-factor analogs were found to partially restore mating to these strains as well, and their relative activities in the mating restoration assay were similar to their activities in the other assays used in this study. Mating was not restored by addition of exogenous a-factor to a cross of a wild-type MAT alpha strain and a MATaste6 mutant, indicating a role of the STE6 gene product in mating in addition to its secretion of a-factor.

Amino Acid Sequence↗
PubMed1991

Repair of Achilles tendon ruptures with a polylactic acid implant: assessment with MR imaging.

An investigational tendon repair device composed of a polymer of lactic acid (PLA) is currently undergoing multicenter clinical trials for use in repairing rupture of the Achilles tendon. The advantages of the PLA device include high tensile strength and the induction of a rapid proliferative tissue response resulting in a shorter rehabilitation period than with conventional surgical repair. We reviewed 16 MR examinations performed in 10 patients 3-35 months after repair to characterize the MR appearance. All 16 T1-weighted sagittal images revealed a thickened fusiform tendon with streaks of moderate signal within the tendon corresponding to the PLA device and its surrounding collagenogenic response. The double-echo T2-weighted axial images at the mid tendon level demonstrated progressive changes in the signal pattern of the central portion of the tendon that reflected the maturation of the healing tendon. All tendons repaired with PLA implants were uniformly hypertrophied relative to the contralateral normal side because of the induced proliferative collagenogenic ingrowth. Two follow-up MR examinations were performed in six patients and showed mean reductions in tendon caliber of 24% and 30% at the mid and inferior levels. MR imaging of the Achilles tendon repaired with PLA implants shows a diffusely thickened tendon with streaks of signal within the tendon that distinguish it from tendons repaired by conventional techniques.

Achilles Tendon↗
PubMed1991

Congenital bifid sternum: repair in early infancy and literature review.

Sternal clefting is an unusual congenital anomaly that should be repaired in early infancy. Early surgery is facilitated by a highly compliant bony thorax. The surgical technique is described, including the (1) removal of a wedge at the confluence of the two lateral sternal bands to allow their apposition, (2) intraoperative assessment of pulmonary compliance and central venous pressure, (3) use of bilateral pectoral flaps, and (4) resulting avoidance of major costochondral stair-step osteotomies. The suggested age of repair is 1 to 4 weeks of age.

Humans↗
PubMed1991

Late functional adaptation after colectomy, mucosal proctectomy, and ileal pouch-anal anastomosis.

Ileal pouch-anal anastomosis (IPAA) is currently an alternative to proctocolectomy and ileostomy for patients with ulcerative colitis or familial polyposis. Some studies have suggested significant anal sphincter damage after mucosal proctectomy. Our aim was to assess prospectively late sphincter function after IPAA. In 250 patients, anorectal pressures were assessed with a pneumohydraulic perfused catheter manometry system. Each patient underwent colectomy, mucosal proctectomy, ileoanal anastomosis of a 15 cm ileal J-pouch, and loop ileostomy. Eight weeks after IPAA, anal manometry was repeated, and the ileostomy was closed. Manometry was repeated at yearly intervals. A decline in resting tone of the anal sphincter occurred early after IPAA with a gradual recovery toward control. External sphincter squeeze after pressures were not affected by IPAA and steadily increased to 8 years after operation. During this time, a progressive increase in J-pouch capacity was noted, and 24-hour stool frequency declined from 7.9 +/- 0.3 stools to 6.5 +/- 0.3 stools (p less than 0.05). We conclude that mucosal proctectomy results in internal anal sphincter trauma but is associated with long-term sphincter recovery, coupled with a significant improvement in external sphincter capacity, ileal pouch volume, and stool frequency.

Adolescent↗
PubMed1990

Total in vitro maturation of the Saccharomyces cerevisiae a-factor lipopeptide mating pheromone.

The a-factor mating pheromone, produced by Saccharomyces cerevisiae a haploid cells, is post-translationally modified in a manner analogous to that of the ras proto-oncogene product. A consensus C-terminal amino acid sequence, -CAAX (C is cysteine, A is aliphatic amino acid, and X is any amino acid), is the target of these modifications, which include isoprenylation (essential for Ras function), proteolysis of the -AAX sequence, and carboxy methyl esterification. Recently, the RAM/DPR1 gene product was shown to be a component of the activity responsible for isoprenylation of both Ras and a-factor. In this report, we present an in vitro assay which not only detects a-factor isoprenylation, but also proteolysis and carboxy methyl esterification, and directly demonstrates, biochemically, the order of these processing events. This a-factor maturation assay may prove useful for screening agents which block any of the steps involved in the post-translational modification of the a-factor and Ras -CAAX sequences. Such agents would be potential anti-Ras-related cancer therapeutic drugs.

Amino Acid Sequence↗
PubMed1990

Synthetic probes for the alpha-factor receptor.

The binding of the tridecapeptide yeast mating pheromone, alpha-factor, to its receptor represents an excellent model for the investigation of peptide hormone-receptor interactions. In this paper we present a number of strategies to probe the binding site of the alpha-factor receptor, and discuss the synthesis of probes containing radioactive and affinity tags. Preferential acylation of the alpha- or epsilon-amine in [Nle12]-alpha-factor was accomplished using 3-[3,5-diiodo-4-hydroxyphenyl] propanoic acid hydroxysuccinimide ester (diiodo Bolton-Hunter reagent). At pH 8.0 in a N-N-dimethylformamide/water mixture the ratio of epsilon- to alpha-acylation was 2.15 to 1, whereas at pH 6.5 in a 1,2-dimethoxyethane/water mixture alpha-acylation was favored by more than 3 to 1. The product distribution was found to depend on pH, organic cosolvent, and the ratio of organic solvent and aqueous buffer. Product distributions were followed using analytical high performance liquid chromatography and the products were characterized enzymatically and by mass spectrometry. Citraconic anhydride preferentially alpha-acylated [Nle12]-alpha-factor and served as a temporary masking group during the synthesis of epsilon-Bolton-Hunter acylated pheromone. Biotin or diiodo Bolton-Hunter reagents were also directly incorporated into [Nle12]-alpha-factor or Lys[Nle12]-alpha-factor during peptide synthesis. The peptides were assembled on a chloromethyl polystyrene resin or on a (phenylacetamido)methyl resin, and cleaved using anhydrous hydrogen fluoride (HF). Probes were inserted on amino groups either prior (biotin) or subsequent (Bolton-Hunter reagent) to HF cleavage. The biological activity of the synthetic peptides was characterized using growth arrest assays.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗
PubMed1990

Substance P stimulates the opossum sphincter of Oddi in vitro.

We have previously shown that substance P (SP) regulates sphincter of Oddi (SO) motility in vivo. However, its mechanism of action remains unclear. Our aim was to develop an in vitro model to measure spikeburst (SB) an contractile frequency (CMC) of the SO and to characterize further SP effects. In 16 opossums, SO rings were excised, mounted within a Kreb's tissue bath with bipolar electrodes and force transducers, allowed to equilibrate, and exposed to increasing SP concentrations with washout between each test solution. Spikeburst and CMC frequencies were recorded on a polygraph, quantitated, expressed as differences before and during SP, and statistically analyzed with Student's test. Although SP induced a significant concentration-dependent increase in phasic SB frequency and CMC, the amplitude of concentrations was not affected by SP. A close correlation was found between basal and SP-stimulated SB and CMC, suggesting myoelectric and mechanical coupling. Previous exposure of SO to SP antagonist [D-Arg1, D-Pro2, D-Trp7,9, Leu11]-SP significantly decreased the response to SP. Tetrodotoxin (TTX), did not affect the delta CMC response to SP. In conclusion an in vitro preparation was developed to study the effect of SP on the SO. Substance P increased SB and CMC of the SO in a concentration-dependent fashion, thus acting as a stimulatory peptide. Perfusion of SO rings with SP antagonist had no effect on basal CMC but significantly inhibited the action of SP in a competitive manner. The effect of SP was not altered by TTX. These data suggest that the action of SP on the SO is primarily myogenic.

Action Potentials↗