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The role of Mn2+ in the reaction catalysed by the galactosyl transferase of bovine milk and colostrum was studied by steady-state kinetic methods at pH 7.4 and 37 °C. The association constants for the binding of Mn2+ by UDP-galactose and by the buffer species used (3-[N-morpholino]propanesulphonate) were measured by electron spin resonance spectroscopy and the concentrations of all the species present in the substrate mixture of Mn2+, UDP-galactose and N-acetylglucosamine were calculated. Previous evidence indicated that high Mn2+ concentrations activate the reaction beyond what is expected from the Michaelis-Menten equation. At such levels (up to 40 mM), the concentration of free Mn2+ was found to be proportional to total Mn within 3%. Experimental data produced as a function of total Mn concentration and total UDP-galactose (i.e. free UDP-galactose plus MnUDP-galactose) concentration could be interpreted in terms of rate equations written in relatively simple form with free Mn2+ and total UDP-galactose concentrations as variables, corresponding to a large variety of kinetic models involving Mn2+, UDP-galactose and MnUDP-galactose as substrates. A group of related mechanisms could not be eliminated at this stage and experiments were carried out in which the concentrations of two of the substrates were varied at either a constant ratio or a constant product depending on how they were involved in the Mn2+: UDP-galactose association reaction. A choice between the two final mechanisms was made by applying statistical non-linear least-squares methods. The most likely mechanism was one in which, after the addition of Mn2+ to the enzyme, the substrates UDP-galactose and MnUDPgalactose added as alternatives to produce two branches, in each of which was added N-acetylglucosamine followed by the release of N-acetyllactosamine, then the Mn2+ complex of UDP, and finally (in the branch in which MnUDP-galactose had been the substrate) free Mn2+. [ABSTRACT FROM AUTHOR]

The article presents a study which examines the profiles of lipids and lipoprotein in a four-hour endurance test on a recumbent cycloergometer. The study involves elite Greek cyclists with the aim of testing their endurance energy capacities divided into two parts, one testing of cardiorespiratory and metabolic capacities and the other one was the lipid indices. Results demonstrate that the four-hour ultraendurance bicycling increases certain lipoprotein and lipid indices.

The nuclear enzyme poly(ADP-ribose) polymerase has been purified about 9200-fold from pig thymus nuclei with a 46% yield. An aqueous organic solvent system was used for the isolation of the polymerase from nuclei and for its purification by chromatography at sub-zero temperatures. Electrophoretic analysis under both denaturing and non-denaturing conditions revealed a single protein band suggesting that the preparation was homogeneous and that the enzyme is composed of one polypeptide chain. The molecular weight estimated from sodium dodecyl sulphate-/polyacrylamide gel electrophoresis was 63500 and from gel filtration through columns of Sephadex G-100, 58000. The enzyme preparation was free from poly(ADP-ribose)-degrading enzymes and from DNA. The purified polymerase showed an absolute requirement for both DNA and histones. The maximal specific activity of the homogeneous preparation measured by the standardized assay, was 20.7 μmol NAD+ incorporated × min-1 × mg-1 of protein at 37 °C. Amino-terminal group analysis with dansyl chloride did not reveal a terminal amino acid suggesting that the amino-terminal group may be blocked. In the presence of histones, the Km for NAD+ was 23 μM. [ABSTRACT FROM AUTHOR]