Activity of phosphatidylethanolamine-N-methyltransferase in brain affectedby Alzheimer's disease

To determine whether phospholipid abnormality in Alzheimer's disease is ass ociated with modification of phosphatidylethanolamine-N-methyltransferase, the activity of the enzyme was analysed in the frontal and occipital cortex of the brain from patients with Alzheimer's disease and from aged-matched control. The optimum pH for phosphatidylethanolamine-N-methyltransferase in human brain was 9.0. The enzyme activity was stimulated by detergent TWEEN 20 but inhibited by Triton X-100. Neither magnesium dependence nor chemica l methylation was found. A decrease in activity of phosphatidylethanolamine -N-methyltransferase was observed in the frontal cortex of brain affected w ith Alzheimer's disease. The addition of exogenous phosphatidylethanolamine resulted in no modification in the methylation rate as compared with that of endogenous PE. The addition of phosphatidyl-N-monomethylethanolamine and phosphatidyl-N,N-dimethylethanolamine resulted in significantly increased rates of methylation in brain tissues. However, the increased rate of phosp hatidylethanolamine-N-methyltransferase activity stimulated by exogenous ph ospholipids was lower in the frontal cortex of brains with Alzheimer's dise ase when compared to the normals and there was no difference in the occipit al cortex between Alzheimer's disease and the control. It is plausible that the decreased activity of phosphatidylethanolamine-N-methyltransferase and its low compensating ability could relate to the modification of phosphati dylcholine in brain tissues from Alzheimer's disease patients. (C) 1999 Els evier Science Ltd. All rights reserved.