Reduced phospholipase D activity in brain tissue samples from Alzheimer's disease patients.

Biochemical examinations of brain tissue samples obtained from patients with Alzheimer's disease have revealed a decreased quantity of the neurotransmitter acetylcholine and reduced activity of choline acetyltransferase (ChAT), the enzyme responsible for acetylcholine formation. It has been suggested that the choline moiety of lecithin, a substitute ubiquitously present in membranes of mammalian cells, could be mobilized for acetylcholine formation. The activity of phospholipase D, an enzyme which releases choline directly from lecithin, was measured in homogenates of Alzheimer brain tissue and found to be reduced by 63%. ChAT activity was reduced by 58% and 5'-nucleotidase activity was reduced by 27% in these homogenates.