Acta biochimica et biophysica; Academiae Scientiarum Hungaricae最新文献

Vanadate in redox state +5 inhibited the Na+K+-activated ATPase as well as the potassium-stimulated p-nitrophenylphosphatase (p-NPPase) activities of plasma membrane fragments prepared from rat brain. Vanadate exhibited a mixed type inhibition on the Na+K+-ATP-ase activity. The same type of inhibition was observed when the p-NPPase activity of the enzyme preparation was measured either in the presence of 20 mM K+ or with 5 mM Na+ + 1 mM K+. When the reaction mixture contained 50 microM ATP, 5 mM Na+ and 1 mM K+, inhibition of p-NPP hydrolised by vanadate displayed a noncompetitive character. Higher noradrenalin concentration was required for counteracting, the inhibition of p-NPPase by vanadate in the presence of ATP than in its absence.

It has been shown previously that at physiological K+-concentrations the development of superprecipitation has a phasic character. Studying the reason of this effect, by the use of beta-32P-ADP ATP-regeneration from ADP was detected during the first phase of superprecipitation. Myokinase activity of actomyosin may be responsible for the appearance of this first phase of turbidity change of actomyosin suspension. Myokinase contributes to the stabilization of an ATP/ADP ratio within narrow limits. During the first phase of superprecipitation the ATP/ADP ratio is between these limits, while during the second phase the ratio has a low value. This phasic evolution of superprecipitation is, probably connected with the physiological functional state of the muscle (contraction or rigour).

The molecular sieving property of human erythrocyte membrane in slightly hypotonic media has been utilized for studying the intracellular localization of some proteins (Cseke et al., 1978, FEBS Lett. 96 15-18). It is now shown that four proteins which appear to be uniformly distributed within the cell behave similarly irrespective of the membrane resistance differences caused by changes of temperature and metabolic energy supply. Five enzymes catalyzing consecutive reactions in the glycolytic pathway between triosephosphate formation and lactate production are released from erythrocytes in quantities deviating from those predicted on the basis of molecular sieving. The data are compatible with the assumption that these enzymes form complexes with each other under in vivo conditions and that complex formation is facilitated if glycolysis is working at high rate (37 degrees C).

Dielectric constant and loss of frog nerve was determined at 6.3 GHz frequency and 20-50 degrees C temperature by a microwave cavity resonator measuring method developed by us. As a result of temperature denaturation the dielectric constant of frog nerve decreases, while its dielectric loss increases. According to our measurements the volume of bound water in nerve is approximately 0.44 ml/l ml dry material. The activation energy of water in the nerve is 16.8 kJ/mol.

A new X-ray microanalyser assembly is described, the main parts of which are a JEOL 100 B transmission electron microscope, a JEOL ASID I scanning attachment, an EDAX 183 B semiconductor detector and a KFKI ICA 70 4k multichannel analyser. By using this equipment, qualitative analysis, equivalent to the original EDAX version, can be performed. Furthermore it is possible to visualize simultaneously the spatial distribution of two or more elements in the sample. The mass of the excited volume of the sample can be determined, independently of the X-ray measurements, by using the electron detector of the scanning attachment. The reproducibility of such measurements is demonstrated and a calibration curve is given. By recording the excited mass of the sample during the X-ray analysis, the damage caused by the exciting electron beam was also examined.

Although the general principles of the chemiosmotic coupling theory have become widely accepted, the (degree of) loc(aliz)ation of electrochemical proton potential difference cannot yet be deduced from the existing experimental data. Many results are not in ready accordance with the idea that one protonic electrochemical potential difference, i.e. the one between a homogeneous inner and a homogeneous outer aqueous phase, would be the high-free-energy intermediate of membrane-linked free-energy transduction. Rather, free-energy transduction in an organelle like a mitochondrion or a chloroplast might take place in large number (about 1 per H+-ATPase) of miniature chemiosmotic systems. The energized protons produced in such a miniature system might be largely (but not totally) confined to a proton-domain belonging to it. Hence, there might be many (rather than one) different relevant proton gradients.

The polynucleotide phosphorylase of Thermus aquaticus was purified using ammonium sulfate fractionation and column chromatography on DEAE-cellulose, heparin-Sepharose 4B and DEAE-Sephadex A25. The enzyme was purified 1500-fold and was 90-95% homogeneous as checked by polyacrylamide gel electrophoresis. It has a molecular weight of 275 000 and consists of four identical subunits. The Km values for the enzyme as determined in polymerization (ADP, GDP, UDP) and phosphorolytic reactions (poly A, poly U) are in the same concentration range as in the case of the enzyme deriving from mesophilic microorganisms. Furthermore, the enzyme is primer dependent and its activity is lost gradually at temperatures higher than 65 degrees C. In the base ratio of the copolymers followed the input base ratio polymerization reactions with polyUA, while with polyAG and polyUG a marked difference between the initial base ratio and the base composition of copolymers was observed.