Acta biochimica et biophysica Hungarica最新文献

In this paper we report on the observation of two parameters of embryonic muscles which show the functional activity of myofibrillar ATPase activity of embryonic muscles and superprecipitation (SP) of natural actomyosin. Our results indicate that, during the embryonic period, the myofibrillar ATPase activity and the SP of actomyosin significantly increased, the rate of this increase being different for leg and breast muscles.

The 60Co gamma-resistance inducing effect of R46 factor, and its elimination by 5-fluorouracil were studied. R46 increased the survival of the wild-type strain and its rec- mutants. After treatment with 5-fluorouracil (1 g/liter) the clones lost not only antibiotic resistance, but the 60Co gamma-radioresistance as well, encoded by R46 R-factor.

Dielectric dispersion effects were studied in purple membranes of different hydration levels. The capacitance and conductivity were measured over the frequency range of 10(2) Hz to 10(5) Hz. With increase in the hydration level, the conductivity increases sharply above the critical hydration of hc = 0.06 g H2O/g protein. This critical hydration is close to the extent of the first continuous strongly bound water layer and is interpreted as the threshold for percolative proton transfer. The capacitance increases continuously with increasing hydration and a larger increase above the water content of 0.1 g H2O/g protein can be seen only at low frequencies. Maxwell-Wagner relaxation also appears above this hydration, showing the presence of a bulk water phase.

Compartmentalization of calcium was studied in frog semitendinosus using 45Ca radioisotope under exchange diffusion condition. Computer based deconvolution was employed to determine the "volume" and the apparent binding constant of the resolved six components. Assuming kinetically parallel and independent compartments nickel treatment slows down the calcium movement through the sarcoplasmic reticulum membrane and for the calcium ions causes competition of the membrane of transverse tubuli and of the sarcoplasmic reticulum. Veratrine treatment caused different effect in the presence and in the absence of sodium ions, demonstrating the essential role of Na+ in equilibrium with Ca2+ exchange processes/ATPases in the Ca2+ uptake and release by sarcoplasmic reticulum. Effect of caffeine and Dantrolene basically opposite on the compartment corresponds to the sarcoplasmic reticulum and similar on the transverse tubuli in term of speed of exchange diffusion.

Adenosine reduced the expression of CD4 antigen both in HIV infected and uninfected H9 T cells. The continuous presence of adenosine (1 mumol/ml) resulted in a remarkable delay of HIV expression in the infected cells. A relationship is suggested in the effects of HIV and adenosine on the human T cells.

The catalytic machineries of serine, cysteine, aspartic and zinc proteases are considerably different. It is pointed out in the light of most recent results that, in spite of the differences, the basic catalytic features of the four types of proteases is common. They all possess a proton carrier (imidazole, carboxylate ion or carboxylcarboxylate diad) which conveys the proton from the attacking nucleophile to the leaving group of the substrate. This uniform strategy facilitates both the formation and the decomposition of the tetrahedral intermediate, and renders regeneration of the enzyme simple.

The kinetic properties dextran-chymotrypsin conjugate were studied by means of low molecular weight substrates. It was found that KM, kcat and kcat/KM of dextran chymotrypsin for the hydrolysis of benzoyl-L-tyrosine-ethyl-ester did not differ substantially from those of the free enzyme. However, the data found for kcat of dextran-chymotrypsin and free chymotrypsin assayed for the hydrolysis of three tripeptidyl-p-nitroanilide D-Arg-Val-Trp-pNA, D-Arg-Val-Tyr-pNA, Z-Phe-Pro-Phe-pNA, were definitely different. The inhibition of the modified chymotrypsin with soybean trypsin inhibitor was found to be less pronounced than that with the free enzyme. The effect of potassium and magnesium salts on the inactivation of both enzymes was also studied. The effect of dextran matrix on the catalytic properties and the conformational stability of modified chymotrypsin is discussed.

Single sodium channel currents were compared in two neuroblastoma (N1E 115, N18) and in two neuroblastoma x glioma (108CC5, 108CC15) hybrid clonal cell lines. Similar single channel parameters were reached from every cell line. The single channel conductance was 11 pS for N1E 115 and N18 cells, and was 10 pS for both hybrid cells at 7-8 degrees C. Except for N18 cells, the amplitude histograms could be best fitted by the sum of two Gaussian functions. The mean channel open time was 1.5-2.0 ms for N1E 115 and the hybrid cells and it was shorter than 1 ms for N18 cells. Open time histograms from N18 cells could be fitted by a single exponential at most potentials, but the sum of two exponentials resulted in a best fit for N1E 115 and the hybrid cells. Differentiation of N1E 115 cells elicited by dibutyryl cAMP instead of dimethylsulfoxide caused only a slight increase in the single channel conductance and open time. The results indicate a certain uniformity of the sodium channels in these cell line.

The Asp102-carboxylate negative charge of the trypsin catalytic-triad has been substituted in part by Cl- counter-ions. A His57-imidazolium cation and Ser195-tetrahedral oxyanion ionpair generated in the acylation step of catalysis is stabilized by the negative charge of Asp102. The importance of correct location of this negative charge has been investigated by experimental analysis of the NaCl influence on the acylation-rate of trypsin, as well as by electrostatic, potential calculations. The acylation-rate was determined with stopped-flow technique under pseudo-first order conditions, by using 4-nitrophenyl-4'-guanidinium benzoate active site titrant at pH 4.25 +/- 0.04, in an unbuffered solution of I = O or 0.5 M NaCl. The acylation-rate constants, kappa 2, are: kappa H2O = 0.32 +/- 0.02 s-1 and kappa NaCl = 3.5 +/- 0.5 s-1, and they correlate to beta-trypsin (the most rapid single-chained form of the enzyme). The rate increasing effect of NaCl, together with the calculated electrostatic energies, indicate that the negative charge contribution of the Asp102-carboxylate to the stabilization of the imidazolium cation and tetrahedral oxyanion intermediate is larger of more orders, than that of the Cl- counter-ion, located in a less favourable position.

The intermediate filament composition of the chorionic villi of the human full-term placenta and that of the amniotic sac was analysed. The analysis of the protein pattern of the Triton X-100 resistant tissue residues on SDS-polyacrylamide gel did not help us in intermediate filament identification because of the protein heterogeneity of the samples. The in vitro polymerization-depolymerization of the detergent resistant tissue proteins did not result in considerable enrichment of the intermediate filament proteins either. The direct immunological identification done by immunoblotting electrophoresis on the detergent resistant tissue residues, revealed that vimentin and cytokeratins were synthetized in detectable quantities in the human extraembryonal tissues.