Acta biochimica et biophysica Hungarica最新文献

The tryptic cleavage process of the sarcoplasmic reticulum Ca(2+)-ATPase was analysed under the influence of experimentally generated membrane potential. The digestion of the Ca2+ transport enzyme was stopped before the dissipation of the potential response. The cleavage products reflected the actual conformation of the enzyme as the low Ca2+ affinity E2, under the influence of inside positive, and as the high Ca2+ affinity E1 conformation under the influence of inside negative potential. These results provide further support for the possible role of transient membrane potential changes in the regulation of the conformational equilibrium of the sarcoplasmic reticulum Ca2+ pump enzyme.

The inactivation of rec BC (D) DNase upon chromatography on DEAE-cellulose was observed. Simultaneously DNA-stimulated ATPases (I and II) and DNase activities on single- and double-stranded DNA substrates were measured in Escherichia coli rec+ and rec- cell extracts. Normal levels of ATPase I and II were detected in rec+ cells. Rec A- cells were lacking DNA dependent ATPase I, while rec B single and rec BC double mutants were defective in DNA dependent ATPase II, the second major enzyme of this type. Rec B and C mutations did not change DNase activities. Rec A mutation significantly increased DNase activity on linear single-stranded substrate.

Comparison of properties of fragmented sarcoplasmic reticulum samples isolated by several methods is reported. It was found that the protein composition does not differ significantly in samples which were or were not washed with 0.6 M KCl when isolated. In the case of samples washed with KCl solution the Zn concentration, the Ca/Mg ratio (determined from experimental data), acetylcholinesterase and superoxide dismutase activities were higher whereas Ca+Mg-activated ATPase and p-nitrophenylphosphatase activities were lower than those of samples which were not washed with 0.6 M KCl. In the latter samples the amount of SH-groups and the reactivity of fast SH-s are higher in Ca+EGTA containing media than in media containing only EGTA. In contrast in the case of samples washed with KCl solution the results are the opposite. In conclusion, washing of FSR with 0.6 M KCl alters the metal composition, enzymatic properties, SH-group reactivity and as a result of these probably the conformation of the protein samples, as well.

The proteolytic degradation products of nasal hyaline cartilage proteoglycans produced by polymorphonuclear leukocyte lysosomal enzymes were investigated. The protein content of the degradation products is 7.0-8.6% corresponding to a peptide chain of 24-28 amino acids and the relative molecular mass of the total fragment is M(r) = 37,600-39,200. On an average, each proteoglycan fragment contains two chondroitin-sulphate chains (M(r) = 22,000-22,400), every fourth fragment contains a keratan sulphate chain (M(r) = 7000-7200) and every seventh to eighth contains an O-glycosidic oligosaccharide. The results of the disaccharide analysis show that the galactosaminoglycan chains contain 76.2-83.6% chondroitin-4-sulphate, 12.9-19.4% chondroitin-6-sulphate, 3.5-3.8% chondroitin and no dermatan sulphate. Since composition and relative molecular mass of the chondroitin sulphate and keratan sulphate chains from the degradation products resemble those from native proteoglycans, it is suggested that the degradation of the proteoglycans occurs by proteinases that attack preferably the chondroitin sulphate region of the core protein.

Phospholipids were separated from 5'-nucleotidase in thyroid plasma membranes by Sephadex G-200 gel filtration. After removal of lipids 5'-nucleotidase was still active and reassociation of the enzyme with phospholipids had a little effect on the increase of enzyme activity. Arrhenius plot of the 5'-nucleotidase activity in native thyroid plasma membranes clearly exhibited a break at 28 degrees C. Biphasic nature of Arrhenius plot showed that the enzyme activity was influenced by physical state of membrane bilayer, although phospholipids were not obligatory cofactor for this enzyme.

A very fast component (life time 0.2 microsecond) was found in the flash-induced absorption changes of bacteriorhodopsin (bR) at 275 nm and 296 nm. This result was obtained by measuring the absorption changes at well defined delay times after the exciting laser flash (590 nm, 20 ns pulse duration). For this purpose a second laser flash was used as the monitoring beam. The very fast absorption changes of bR in the UV range are due to the rapid perturbation of the opsin moiety near the chromophore, as a result of the all-trans to 13-cis isomerization of the retinal taking place on the same time scale.

Yeast alcohol dehydrogenase (alcohol: NAD+ oxidoreductase, EC 1.1.1.1) was adsorbed onto polyethylene terephthalate, a synthetic polymer. The effects of the polymer on the properties of the enzyme were studied. The specific activity of the bound enzyme on protein basis was only 1.2 per cent of the specific activity of the soluble enzyme. The optimum pH for the catalytic activity was strongly shifted toward acidic direction. The apparent temperature optimum of the bound enzyme was identical with that of the soluble form. The apparent Michaelis constants of the bound enzyme were higher for both ethanol and NAD+. The conformational stability of the enzyme against heat treatment and urea was decreased as a consequence of adsorption.

An enzyme isolated from Ehrlich ascites plasma and capable of cleaving trypsin active site titrant 4-nitrophenyl-p-guanidinobenzoate (Steven, F.S. and Al-Achmad, R.K. (1983) has been further investigated. The substrate hydrolysis follows Michaelis-Menten kinetics. The molecular mass of the enzyme is 50-70 kDa by gel filtration and SDS polyacrylamide gel electrophoresis. It has the mobility of albumin and coelutes with a carboxylesterase activity on a cation exchange column. (Cbz-Arg-NH)2-Rhodamine, the specific noncompetitive inhibitor of guanidinobenzoatase, also inhibits the carboxylesterase activity. Therefore, the guanidinobenzoatase activity of Ehrlich ascites plasma is a carboxylesterase (EC 3.1.1.1.) which likely originates from blood.