Lipid peroxidation inhibits oleoyl-CoA: 1-acyl-sn-glycero-3-phosphocholine O-acyltransferase in rat CNS axolemma-enriched fractions.
The effect of phospholipid peroxidation on the acylation of lysoPtdCho (lysophosphatidylcholine) by axolemma-enriched fraction prepared from rat brain stem was investigated. After two types of peroxidative treatments, the in vitro induction of malondialdehyde and conjugated dienes formation in axolemmal membranes correlated to a shift in the ratio of saturated/unsaturated fatty acids. By using an Fe2+ (20 microM)-ascorbate (0.25 mM) peroxidation system, the residual acyltransferase activity was 55% of the initial one. No change in Km value for either oleoyl-CoA or lysoPtdCho was found, whereas a loss of 24% in Vmax was observed. After 5 min preincubation with 150 mM t-BuOOH, 70% inactivation of the acylation reaction was observed. A near suppression of enzyme activity was reached with 400 mM. The apparent Km for oleoyl-CoA decreased sharply (from 6.6 microM in control preparations to 4.1 microM in t-BuOOH-treated membranes), indicating a 2-fold increase in the enzymatic affinity for this substrate. The apparent Km for lysoPtdCho increased markedly (from 1.56 microM in the control preparations to 5.88 microM in t-BuOOH-treated membranes) whereas a decrease of Vmax (from 1.65 to 0.80 nmol/min/mg protein) for the same substrate was observed. Significant enzyme inactivation (loss of 60% of initial activity) was seen when 10 mumol of photooxidized phospholipids were preincubated with axolemmal membranes. Significant dose-dependent enzyme inactivation was brought about by addition of 10-60 mumol of peroxidized PtdEtn/100 micrograms axolemmal protein. The percent enzyme inhibition by peroxidized PtdCho at equivalent amounts was lower than that by PtdEtn.(ABSTRACT TRUNCATED AT 250 WORDS)
Alberghina
M
M
Institute of Biological Chemistry, Faculty of Medicine, University of Catania, Italy.
Lupo
G
G
Anfuso
C D
CD
D000217:Acyltransferases / Q000037:antagonists & inhibitors*; D000818:Animals; D001205:Ascorbic Acid / Q000494:pharmacology*; D001369:Axons / Q000378:metabolism*; D001933:Brain Stem / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D005260:Female; D005290:Ferric Compounds / Q000494:pharmacology*; D007700:Kinetics; D015227:Lipid Peroxidation; D008297:Male; D008563:Membrane Lipids / Q000302:isolation & purification / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley
D005290:Ferric Compounds; D008563:Membrane Lipids; C061126:iron(III)-ascorbic acid complex; D000217:Acyltransferases; C031076:2-acylglycerophosphocholine acyltransferase; D001205:Ascorbic Acid