Biomedica biochimica acta最新文献

Proteasomes isolated and purified from rat muscle tissue and from the archaebacterium Thermoplasma acidophilum have a very similar size and shape, but the subunit composition is less complex in the archaebacterium as compared to the eukaryotic particle. The archaebacterial enzyme contains a catalytic site with chymotryptic specificity, which is inhibited by serine proteinase inhibitors and clearly differs from the eukaryotic particle which has a minimum of three catalytic sites for peptide bond hydrolysis of a yet undefined mechanism.

Three genes from the human cystatin gene family have been isolated from a bacteriophage lambda library containing Hind III digests of human genomic DNA. The cloned genes were identified with three DNA probes each containing exon 1, exon 2 and exon 3 of the CST1 gene for cystatin SN. The genes, which we name CST2B, CST4, and CST5, are 6.8 kb, 5.4 kb and 12.5 kb in size, respectively. Statistical analysis of DNA sequence homology elucidated that the second and third exons of cystatin (family II) genes and three cystatin (family II) gene like segments in the kininogen (family III) genes are significantly homologous to the gene segments coding for the inhibitory domains of Bowman-Birk type proteinase inhibitors.

A cloned synthetic gene coding for (AEF S1M M29I M89L) chicken egg white cystatin was modified site-specifically at position Q53 by cassette mutagenesis. Two recombinant variants were isolated from a pIN-III-ompA E. coli expression system and purified by Cm-papain affinity chromatography. The mutations at the position 53 were confirmed by amino acid composition and amino acid sequence analysis of the appropriate tryptic peptides. The complexes of both cystatin variants, the Q53E- and Q53N-variant with papain, display Ki values similar to those determined with native chicken cystatin. However, the Ki values of the complexes with actinidin are hundredfold and with cathepsin B three hundredfold higher than with the native chicken cystatin. The different inhibition kinetics of these variants compared to wild type chicken cystatin emphasizes the specificity of single amino acid substitutions for optimal contacts between the binding segments of enzyme and inhibitor.

The role of water in mainly organic reaction mixtures for biocatalysis is best analysed in terms of the thermodynamic water activity. This determines water mass action effects on the equilibria of protease-catalysed peptide or ester synthesis. It can also be useful to predict the amount of water bound by the enzyme, and hence its catalytic activity, as other factors are changed.

The synthesis of the chromogenic substrates for trypsin-like proteinases catalyzed by alpha-chymotrypsin and subtilisin from B. subtilis strain 72 were carried out in the organic media at a low water content using the enzymes adsorbed on different porous materials. The method proposed allows us to vary the structure of the compounds to be synthesized and is a suitable technique for their scaling-up.

The alpha-glyceryl esters of Z-Gly, Z-Phe and Z-Tyr were synthesized and their use for protease catalyzed peptide synthesis was studied. Three enzymes isolated from crude papain were compared in their catalytic potency. Syntheses with alpha-chymotrypsin were performed in a biphasic system.

Several amino acid derivatives with the negatively charged N alpha-protecting groups Maleyl (Mal) and Citraconyl (Cit) were synthesized and used in enzyme-catalyzed peptide synthesis. Compared to commonly used alpha-amino protecting groups in chemical peptide synthesis (Z, Fmoc, Boc, etc.), these charged protecting groups strongly increase both water solubility of different aromatic amino acid derivatives and activities of synthesis reactions. As a consequence of the solubilizing effect, we used these groups in the kinetically controlled peptide synthesis choosing kyotorphin (tyrosyl-arginine) as a model peptide. With Mal-Tyr-OEt as substrate and Arg-OEt as nucleophile, we succeeded in the alpha-chymotrypsin-catalyzed production of about 12 kg of Tyr-Arg (50.4% overall yield) in a 300 l batch experiment.

Alterations in the erythrocyte rheology and the contents of activated free radical oxidation products (conjugated dienes, products of thiobarbituric acid and Schiff bases) in the acute phase of experimental thermic injury of the skin were studied. Erythrocyte flexibility reduction and erythrocyte aggregation increase correlated with elevated amounts of free radical oxidation products. Alpha-tocopherol avoided the accumulation of free radical oxidation products and improved both antioxidant defence and erythrocyte rheology. Thus we suppose that free radical oxidation products probably participate in the pathogenesis of erythrocyte rheology disturbances after thermic trauma.

A phospholipase C was solubilized and purified from membranes of porcine brain cortex. Simultaneously, a phospholipase C was purified from a cytosolic fraction of porcine brain cortex. The enrichment of phospholipase C from either fraction was about 1000-fold as determined by hydrolysis of phosphatidylinositol 4,5-bisphosphate. Phospholipases C purified from membranes or from cytosol were indistinguishable with regard to the following properties: The enzyme activities copurified with a protein of 145 kDa. The standard sedimentation coefficients (s20,w values) of the purified enzymes were 6.2 S in the absence or presence of 0.3% (w/v) sodium cholate; Stokes' radii, estimated by gel filtration on a Superose 6 HR 10/30 column in the presence of 0.3% sodium cholate, were 4.5 nm; calculated molecular masses were about 120 kDa; no significant hydrolysis of phosphatidylcholine, phosphatidylethanolamine and phosphatidylserine by preparations of purified phospholipase C was observed; adenine and guanine nucleotides affected the activity of purified enzymes in a complex manner. Thus, the enzymes purified from membraneous and from cytosolic fractions exhibited properties of the phospholipase C-beta form. The enzymes purified from either fraction required Ca2+ at a low concentration (100 nM to 10 microM) for maximal activity. The advantage of the present purification procedure is that the purified enzymes were free of phosphatidylinositol 4,5-bisphosphate 5-phosphatase, inositol 1,4,5-trisphosphate 5-phosphatase and guanine nucleotide-binding proteins after three chromatographic steps. The purified enzymes may, therefore, prove useful for studying the hormonal regulation of phospholipase C in reconstituted systems and for the preparation of [5-32P]inositol 1,4,5-trisphosphate from [5-32P]phosphatidylinositol 4,5-bisphosphate.

The ability of ascorbic acid (AA) (25 to 500 microM) to increase OH production by a chemical (Fe(2+)-EDTA-H2O2), an enzymatic (xanthine-xanthine oxidase-Fe(2+)-EDTA) and a cellular system (3.10(6) human polymorphonuclear leukocytes (PMNL) or murine peritoneal macrophages (PM) activated with 7.2 ng PMA/ml) was studied. At all concentrations used AA strongly enhanced OH generation by the chemical and the enzymatic systems. However, the maximal increase of about 14-fold was found for incomplete chemical system (10 microM Fe(2+)-20 microM EDTA) and 500 microM AA. In the case of phorbol-myristate-acetate-activated-PMNL and macrophages, the moderate increase in OH formation was only caused by low AA concentrations. At 50 microM AA, the OH formation was 112 +/- 3 and 117 +/- 4% of control, respectively. Higher AA concentrations had no influence or even decreased OH formation by phagocytes. It is suggested that administration of AA will not significantly enhance OH generation from pulmonary phagocytes and could be useful for prevention of the oxidant-mediated lung injury related to inflammation.