ABSTRACT
Soluble nucleoside triphosphatase differing in its properties from all known proteins with NTPase activity was partially purified from bovine kidneys. The enzyme has pH optimum of 7.5, molecular mass of 60 kDa, as estimated by gel chromatography, and shows an absolute dependence on divalent metal ions. NTPase obeyed Michaelis-Menten kinetics in the range of substrate concentration tested from 45 to 440 microM; the apparent Km for inosine-5'-triphosphate was calculated to be 23.3 microM. The enzyme was found to possess a broad substrate specificity, being capable of hydrolyzing various nucleoside-5'-tri- as well as diphosphates.
Subject(s)
Kidney/enzymology , Nucleoside-Triphosphatase , Animals , Catalysis , Cattle , Chromatography, Gel , Hydrogen-Ion Concentration , Inosine Triphosphate/metabolism , Kinetics , Molecular Weight , Nucleoside-Triphosphatase/isolation & purification , Nucleoside-Triphosphatase/metabolism , Nucleoside-Triphosphatase/physiology , Nucleotides/metabolism , Solubility , Substrate SpecificityABSTRACT
The levels of phosphate esters and the activities of thiamine biotransformation enzymes in the blood and tissues of albino rats were studied during oxythiamine-induced B1 deficiency and after metabolic correction with thiamine and taurine. Among thiamine phosphates, the most informative indicators of thiamine deficiency were shown to be triphosphate esters and free thiamine diphosphate. The biosynthetic enzymes thiamine kinase and thiamine diphosphate kinase played a decisive role in maintaining the initial rate and in recovering the physiologically active forms of vitamin B1. The activation of hydrolytic enzymes of thiamine phosphate esters occurred by producing abundant free thiamine diphosphate and thiamine triphosphate. Within the first hours, taurine favoured the acceleration of phosphoester biosynthesis and, accumulating in the tissues, inhibited vitamin phosphorylation reactions.
