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R Friesen

Publications and source records attributed to R Friesen.

9 recordsLinked to original sources
PubMed2001

The YRD motif is a major determinant of substrate and inhibitor specificity in T-cell protein-tyrosine phosphatase.

We have studied T-cell protein-tyrosine phosphatase (TCPTP) as a model phosphatase in an attempt to unravel amino acid residues that may influence the design of specific inhibitors. Residues 48--50, termed the YRD motif, a region that is found in protein-tyrosine phosphatases, but absent in dual-specificity phosphatases was targeted. YRD derivatives of TCPTP were characterized by steady-state kinetics and by inhibition studies with BzN-EJJ-amide, a potent inhibitor of TCPTP. Substitution of Asp(50) to alanine or Arg(49) to lysine, methionine, or alanine significantly affected substrate hydrolysis and led to a substantial decrease in affinity for BzN-EJJ-amide. The influence of residue 49 on substrate/inhibitor selectivity was further investigated by comparing subsite amino acid preferences of TCPTP and its R49K derivative by affinity selection coupled with mass spectrometry. The greatest effect on selectivity was observed on the residue that precedes the phosphorylated tyrosine. Unlike wild-type TCPTP, the R49K derivative preferred tyrosine to aspartic or glutamic acid. BzN-EJJ-amide which retains the preferred specificity requirements of TCPTP and PTP1B was equipotent on both enzymes but greater than 30-fold selective over other phosphatases. These results suggest that Arg(49) and Asp(50) may be targeted for the design of potent and selective inhibitors of TCPTP and PTP1B.

Amino Acid Substitution↗
PubMed1995

Microsomal metabolism of the 5-lipoxygenase inhibitors L-746,530 and L-739,010 to reactive intermediates that covalently bind to protein: the role of the 6,8-dioxabicyclo[3.2.1]octanyl moiety.

Hepatic microsomes from different species were used to study the oxidative metabolism of L-746,530 and L-739,010, two potent and specific 5-lipoxygenase inhibitors. HPLC analysis of the incubates obtained from the microsomal incubations of L-739,010 and L-746,530 showed only traces of metabolites. However, recovery of the starting material in the supernatant was less than quantitative in all of the species studied (approximately 90% in rat, approximately 70% in the dexamethasone-induced rat, approximately 70-90% in humans, and approximately 60% in the rhesus monkey for both compounds). The recovery of the starting material was found to be time- and NADPH-dependent, suggesting that metabolite(s) were formed and reacting with the microsomal proteins. Evidence that the cytochrome P4503A (CYP3A) contributed to the formation of the reactive metabolite(s) was shown by the low recovery of material that was observed upon incubation with microsomes obtained from dexamethasone-treated rats (a CYP3A inducer), compared with microsomes obtained from untreated rats. Also, the recovery of material was improved when troleandomycin, a CYP3A inhibitor, was added to rhesus monkey microsomal incubations (25% more parent compound detected in the supernatant with 100 microM of troleandomycin). Using radiolabeled L-746,530 and gel electrophoresis analysis, it was confirmed that radiolabeled material was covalently bound to the microsomal protein. Incubations of L-739,010 and L-746,530 in the presence of semicarbazide resulted, in both cases, in the formation of two adducts. Using a combination of NMR, liquid secondary-ion MS, and UV techniques, these adducts were identified as isomers of an oxidized metabolite that had been trapped by semicarbazide. The site of oxidation was determined to be on the dioxabicyclo moiety. The importance of this moiety in the formation of reactive metabolite(s) was verified by incubating analogs of the 5-lipoxygenase inhibitors that contained blocking methyl groups at the proposed site of oxidation on the bicyclo moiety. Incubations of these gemdimethyl analogs of L-746,530 and L-739,010 with microsomes from different species resulted in significantly improved recovery of the starting material (approximately 94% in the rat, 85% in the dexamethasone-induced rat, 95% in humans, and 85% in the rhesus monkey for both compounds) and significantly less radioactive binding to the microsomal protein.

Animals↗
PubMed1992

Colorectal leiomyosarcomas: a pathobiologic study with long-term follow-up.

Colorectal leiomyosarcoma (CLM) is an uncommon tumour. Reports of its occurrence have been published mostly as single cases or small series. This study documents 12 cases of CLM that were seen over a 28-year period in Saskatchewan. The annual incidence of CLM was 0.45 per million people and constituted 0.12% of all colorectal malignant tumours seen during the study period. CLMs had a predilection for the rectum and sigmoid and commonly were associated with rectal bleeding or abdominal pain. More than half the tumours were detected by sigmoidoscopy. A correct preoperative or intraoperative histologic diagnosis of leiomyosarcoma was made in only two out of six cases. A potentially curative surgical procedure was done in 10 of the 12 patients. The mean follow-up was 6.9 years. Eight patients had tumour recurrence or metastasis, or both. From the findings of this study the authors recommend wide excision of colorectal smooth-muscle tumours whenever there is a suggestion of malignancy.

Adult↗
PubMed1991

Measurement of cardiac output--transtracheal Doppler versus thermodilution.

The ABCOM 1 transtracheal Doppler (TTD) has been developed as a non-invasive cardiac output monitor. With this device, cardiac output is continuously calculated from ascending aortic blood flow velocity and aortic diameter obtained via an ultrasound transducer incorporated into the tip of an endotracheal tube. We evaluated the clinical use of the ABCOM 1 monitor and compared cardiac outputs obtained using the TTD system with simultaneous thermodilution (TD) measurements. We found the operation of the ABCOM 1 monitor to be difficult and time-consuming. In our operating rooms, acceptable Doppler signal quality was difficult to obtain. There was no correlation between 36 simultaneously obtained TTD and TD cardiac output measurements. The average difference between measurement techniques and the limits of agreement were unacceptably large (mean difference = 3.04 L.min-1, mean +/- 2 SD = -6.04 to 12.48 L.min-1). Separately analyzing only those measurements during which Doppler signal quality was adequate did not improve agreement between TTD and TD measurements. On the basis of these findings, TTD cannot be recommended as a clinical cardiac output measurement technique.

Cardiac Output↗
PubMed1991

Colorectal smooth-muscle tumors. A pathobiologic study with immunohistochemistry and histomorphometry.

Smooth-muscle tumors are an interesting group of tumors that show considerable site specificity in their pathobiology. Recent work has also shown that some previously so-called smooth-muscle tumors were not, in fact, truly leiomyogenic, hence the origin of the more embracing term stromal tumors. The purpose of this retrospective study was to delineate the tumor subsets constituting colorectal stromal tumors, and to determine the histopathologic correlates for biologic aggressiveness for these tumors. The cohort was constituted of 12 patients; the mean follow-up was 6.6 years with a median of 5.0 years. Immunohistochemical evaluations showed tumoral positivity for muscle-specific actin (12 of 12), vimentin (11 of 12), desmin (two of 12), and S100 protein (zero of 12). Electron microscopic examinations corroborated this leiomyogenicity profile (five of five). Semiquantitative histomorphometric analysis showed that tumor size, cellularity, mitoses, and necrosis, in that order, correlated with biologic aggressiveness. The immunohistochemistry results for this cohort of colorectal stromal tumors vindicated the traditional histochemical evaluations in that all tumors showed features of leiomyogenicity. For colorectal smooth-muscle tumors, tumor size appears to be the best predictor for biologic aggressiveness. This study reinforces the concept of site-specificity for smooth-muscle tumors.

Adult↗
PubMed1989

Induced abortion.

Explore the source record for details and available documents.

Abortion, Induced↗
PubMed1981

Surgical repair of coarctation of the aorta in infants less than six months of age: including the question of pulmonary artery banding.

High mortality rates (20% to 60%) have been reported in the repair of coarctation of the aorta in infancy. During a 4 year period, 34 infants less than 6 months of age had coarctation repair (two prior to 1976). Eleven were less than 2 weeks of age, nine were 2 weeks to 1 month, eight were 1 to 2 months, and six were 2 to 6 months. Associated lesions were patent ductus arteriosus (PDA) (82%), ventricular septal defect (VSD) (53%), and other intracardiac lesions (35%). Twenty-three patients (67%) had emergency operations; the other procedures were semielective. The indications for operation included congestive cardiac failure (91%), acidosis (32%), hypertension (29%), cardiogenic shock (26%), and cardiac arrest (18%). There was one operative death (2.9%) in a patient with severe pulmonary valve insufficiency and multiple VSDs. There was one late death a 4 months (Taussig-Bing complex). Primary repair was used in 15, patch-graft angioplasty in 19 (left subclavian artery in nine, left common carotid in one, and Dacron or pericardial patch in nine). Two (6%) required reoperation for recurrent coarctation (follow-up 3 to 36 months with a mean of 25.8). Of 15 patients with a large VSD, six had pulmonary artery banding with two deaths (one operative and one late), two had debanding plus VSD repair, and two are awaiting operation. The remaining nine patients did not have banding (no operative or late deaths), four patients required late VSD closure, two VSDs closed spontaneously, two VSDs became smaller, and one patient is awaiting VSD closure. The infrequent need for pulmonary artery banding may be partly due to "physiological banding" seen at Denver's high altitude. The VSD spontaneously closed or became smaller in 44% of nonbanded patients. The low operative mortality can be ascribed to (1) aggressive medical therapy, (2) emergency catheterization and repair, (3) avoidance of hypothermia, and (4) adequate relief of the coarctation.

Aorta↗
PubMedDate not supplied

Manipulation of activity and orientation of membrane-reconstituted di-tripeptide transport protein DtpT of Lactococcus lactis.

The di-tripeptide transport system (DtpT) of Lactococcus lactis was purified to apparent homogeneity by pre-extraction of crude membrane vesicles with octaethylene glycol monodecyl ether (C10E8), followed by solubilization with n-dodecyl-beta-D-maltoside (DDM) and chromatography on a Ni-NTA resin. The DtpT protein was reconstituted into detergent-destabilized preformed liposomes prepared from E. coli phospholipid/phosphatidylcholine. A variety of detergents were tested for their ability to mediate the membrane reconstitution of DtpT and their effectiveness to yield proteoliposomes with a high transport activity. The highest activities were obtained with TX100, C12E8 and DM, whereas DDM yielded relatively poor activities, in particular when this detergent was used at concentrations beyond the onset of solubilization of the preformed liposomes. Parallel with the low activity, significant losses of lipid were observed when the reconstitution was performed at high DDM concentrations. This explained at least part of the reduced transport activity as the DtpT protein was highly dependent on the final lipid-to-protein ratios in the proteoliposomes. Consistent with the difference in mechanism of DDM- and TX100-mediated membrane protein reconstitution, the orientation of the DtpT protein in the membrane was random with DDM and inside-in when TX100 was used. The methodology to determine the orientation of membrane-reconstituted proteins from the accessibility of cysteines for thiol-specific reagents is critically evaluated.

Bacterial Proteins↗