Biochemistry international最新文献

Chitinase has been purified from the extract of cabbage through successive steps of ammonium sulfate fractionation, chromatofocusing and Sephadex G-75 gel filtration. By these steps, the purity of the enzyme increased by 93.3 fold and the recovery of the enzyme activity was 20%. The purified enzyme had an optimal pH of 5.0, an optimal temperature between 40 to 50 degrees C and a Km of 76 microM for hydrolysis of ethylene glycol chitin. The molecular weight of the enzyme determined from filtration through Sephadex G-75 was 30,000 daltons. Heavy metal ions, Hg2+ (0.5 mM) and Ag+(2.5 mM) significantly inhibited the activity of the enzyme. NBSI1 (1.0 mM), DNFB (0.5 mM) and PMSF (0.5 mM) completely inhibited the activity of the enzyme. The enzyme also showed muramidase activity for hydrolysis of Micrococcus lysodeikticus cell wall. The presence of chitinase in cabbage may function as a defense enzyme against potential pathogens.

The nucleotide sequence of a cDNA for porcine heme oxygenase was determined. The open reading frame encoded a polypeptide of 288 amino acid residues with a molecular mass of 33,074 Da. A prokaryotic expression plasmid carrying porcine heme oxygenase cDNA was constructed and transfected into Escherichia coli cells. The full-length heme oxygenase expressed was localized in the bacterial membranes. Two small-sized heme oxygenases with no membrane-bound properties were also detected, suggesting that in E. coli cells a considerable amount of the enzyme expressed was degraded.

Extracellular beta-glucosidase was purified from a white-rot fungus, Trametes gibbosa by 50% ammonium sulphate saturation and Sephadex G-100 column chromatography. It showed maximum activity towards p-nitrophenyl- beta-D- glucopyranoside (pNpG). The pH optimum was 3.5. Temperature optimum was 40 degrees C but shifted to 50 degrees C on preincubation with pNpG. Hg2+, Fe3+ and Cu2+ strongly inhibited the activity. The enzyme was competitively inhibited by glucose with a Ki of 5.2 mM. The apparent molecular mass as determined by gel filtration chromatography was 640 kDa.

Hormonal control of rat uterine collagenase activities which use collagen types I, III, and V as the substrates has been studied. The collagenases are shown to be regulated in general by estradiol as well as by progesterone. However, the enzyme activity that uses type III collagen as the substrate appears to have a preferential response to progesterone over estradiol.

Organic hydroperoxides induce oxidative damage to mammalian cells. We describe how luminol-amplified chemiluminescence can be used to monitor free radical generation (following treatment of erythrocytes in vitro with organic hydroperoxides) throughout the entire time-course of oxidative stress. Enrichment of erythrocyte alpha-tocopherol levels increased the induction time by 25% and led peak chemiluminescence fall of 30%. Furthermore, ascorbate loading reduced the signal four-fold during the induction period. The catalytic role of haemoglobin was shown by the abolition of chemiluminescence by azide and a low (but detectable) signal in haemoglobin-depleted erythrocyte ghosts. Luminol-amplified chemiluminescence enables the kinetics of free radical generation to be monitored continuously. Furthermore, it may enable features of the mechanism of interaction between cellular antioxidants and antioxidant enzymes to be elucidated.