Biomedical subjects
Publications and source records attributed to L Guenet.
Proteases are enzymes which are widely distributed in cells and play a key role in protein metabolism. The aim of this paper is to review the classification and nomenclature of proteases, their catalytic mechanisms, the regulation of proteolytic activity and finally the major biological functions of proteases.
The effects of fasting, diabetes, cholestasis, two-third hepatectomy and adrenalectomy on the rat liver plasma membrane serine proteinase activity were studied. Our results show a significant decrease of the enzyme activity during fasting (-50%), during experimental diabetes (-50%), in regenerating liver after partial hepatectomy (-70%) and after extrahepatic cholestasis (-70%). No modifications are noted when the rats are bilaterally adrenalectomized. These findings suggest that the enzyme activity may be linked to the level of circulating insulin, and may be regulated in physiological cellular proliferation so as to prevent undesirable protein degradation.
Perhexiline is a lysosomotropic agent which has proved to be very valuable to certain patients suffering from angina pectoris. However long-term administration of the drug may induce hepato- and neuro-toxicity. Using HTC cells (a rat hepatoma-derived cell line) whose plasma membranes were labeled with NaB[3H]4 after oxidation by NaIO4, endocytosis and recycling of labeled asialo-orosomucoid (ASOR) receptors were investigated in the presence of 50 mumols/l perhexiline maleate. The results demonstrate that the drug induces a significant decrease of the rate of both the internalization and the recycling of ASOR receptors. The mechanisms responsible for these effects have not yet been elucidated. However, the current findings may be related to the previously observed inhibitory effect of perhexiline on cellular (Na+, K+)-ATPase and Mg++-ATPase activities. Our findings would then reflect insufficient cellular energy production, resulting from depressed ATP hydrolysis in the presence of perhexiline.
Human clinical observations and in vivo studies have shown that the amphiphilic drug perhexiline maleate is responsible for lipidosis storage disorders. When the drug was incubated in vivo with rat brain homogenates, the ouabain-sensitive (Na+,K+)-ATPase and the Mg++-ATPase activities were inhibited. 50% inhibition occurred at the drug concentrations 5.10(-5) M for (Na+,K+)-ATPase and at 10(-4) M for Mg++-ATPase, respectively. Kinetic studies performed on rat brain homogenates showed a mixed type inhibition of these enzymes by perhexiline maleate. The effect of other lysosomotropic drugs (imipramine, chlorpromazine, thioridazine and tamoxifen) on (Na+,K+)-ATPase and on Mg++-ATPase activities was found to be similar to that induced by perhexiline maleate. These results indicate that the inhibitory effect of perhexiline maleate on (Na+,K+)-ATPase and Mg++-ATPase may be a common feature shared by the lysosomotropic drugs.
A serine endopeptidase was partially purified from rat liver plasma membranes by using a four-step procedure: solubilization with N-lauroylsarcosine; Ultrogel AcA-34 chromatography; CM Affi-Gel blue chromatography; agarose-soybean trypsin inhibitor chromatography. This enzyme was found to hydrolyze casein and various chromogenic peptide substrates; highest activity occurred with H-D-Val-Leu-Arg-p-nitroanilide, reported to be a specific substrate for human glandular kallikreins. The enzyme was heat-sensitive, showed a pH optimum between 8.0 and 9.0 and was inhibited by D-Phe-L-Phe-L-Arg-CH2Cl, aprotinin, diisopropyl fluorophosphate (DFP), soybean trypsin inhibitor, phenylmethylsulphonyl fluoride, leupeptin, antipain and dithiothreitol. This liver plasma membrane proteinase has an apparent molecular weight of about 30 000 as determined by Ultrogel AcA-34 chromatography and by autoradiography of [3H]DFP-labelled protein electrophoresis.
The authors have studied the genetic polymorphism of the properdin factor B (Bf) by the isoelectrofocusing technique. The SS phenotypes, all similar on agarose gel electrophoresis, were shown to be heterogeneous after isoelectrofocusing; this heterogeneity corresponds to the expression of two new suballeles SA and SB, inherited in a codominant manner. Gene frequencies for 121 individuals with SS phenotype are 0.57 for SA, and 0.43 for SB.
Disagreement concerning serum angiotensin-converting enzyme (ACE) levels in patients with chronic renal failure has been observed in recent reports. Because ACE is considered as a useful tool for the diagnosis and management of sarcoidosis, and because chronic renal failure may be associated with sarcoidosis, the present work was designed to reinvestigate the possible changes of serum angiotensin-converting enzyme activity in a series of 36 non-hemodialysed consecutive patients with chronic non-sarcoid renal failure. Enzyme activity was significantly lower (p less than 0.004) in the patients (15.8 +/- 5.0 units/ml, mean value +/- 1 SD) than in 47 healthy controls (20.2 +/- 7.6 units/ml, mean value +/- 1 SD). Serum angiotensin-converting enzyme and creatinine clearance values were significantly correlated in these patients (p less than 0.0002). These results indicate that, in non-hemodialysed patients with chronic renal failure, serum angiotensin-converting enzyme levels may not be useful in establishing the diagnosis of sarcoidosis.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Forskolin, a natural diterpene, is a novel, potent activator of a variety of adenylate cyclase systems; its mechanism and site of action are still disputed. We report here that, while forskolin activates liver adenylate cyclase up to 15-fold, it does not activate cyclase of ram sperm which comprises a pure catalytic subunit. However, forskolin activation of sperm adenylate cyclase activity could be observed after reconstitution with the regulatory component-enriched membrane from human erythrocytes. The diterpene weakly (3-5-fold) activated the cytosolic, soluble cyclase found in rat and ram tests, but this effect was lost when the cyclase was purified by gel chromatography. Our data are not compatible with the hypothesis that forskolin acts directly on the catalytic subunit, but rather suggest that it acts via another regulatory component, part of, or different from, the GTP-binding regulatory complex.