ABSTRACT
Rats were chronically intoxicated with triethyltin in the drinking water (0.002%) for a period of 15 days. Starting with day 5 of the intoxication period a decrease in the body weight was observed and, in parallel, the development of a cerebral oedema could be followed by measuring white matter density. At the same time, an increase of phosphatidylethanolamine-N-methyltransferase and cholinephosphate cytidylyltransferase activities was noted. This increase might be a compensatory mechanism for counteracting the membrane damages induced by triethyltin.
Subject(s)
Brain/enzymology , Cytidine Triphosphate/metabolism , Cytosine Nucleotides/metabolism , Nucleotidyltransferases/metabolism , Trialkyltin Compounds/toxicity , Triethyltin Compounds/toxicity , Animals , Body Weight/drug effects , Brain Edema/physiopathology , Chloroform , Choline-Phosphate Cytidylyltransferase , DNA/metabolism , In Vitro Techniques , Male , Membranes/metabolism , Methylation , Methyltransferases/metabolism , Nerve Tissue Proteins/metabolism , Rats , Rats, Inbred Strains , Subcellular Fractions/drug effects , Subcellular Fractions/metabolismABSTRACT
In order to investigate the mechanisms involved in some brain disorders at the membrane level, we studied the kinetics and biochemical properties of brain CTP:choline-phosphate cytidylyltransferase (EC 2.7.7.15), the rate-limiting enzyme of the two-step biosynthesis of phosphatidylcholine. This enzyme catalyzes the biosynthesis of CDPcholine from choline phosphate and CTP. We found that its subcellular localization (mainly in microsomal and cytosolic fractions) was different from that of phosphatidylethanolamine N-methyltransferase (EC 2.1.1.17), the enzyme of the alternative pathway for phosphatidylcholine synthesis. CTP:choline-phosphate cytidylyltransferase showed a Km of 10 mM for CTP and 0.3 mM for choline phosphate and exhibited a random mechanism. CDPcholine, the reaction product, was a competitive inhibitor of choline phosphate and CTP utilization and had a Ki of 0.090 mM. Both particulate and soluble enzymes required Mg2+ and exhibited an optimal pH at about 7. Cytosolic activity was enhanced by addition of unsaturated fatty acids or phospholipids extracted from brain membranes. Such an enhancement was increased with the centrifugation time used for preparing the soluble enzyme.
