PHOSPHOLIPASE-D ACTIVITY OF RAT-BRAIN NEURONAL NUCLEI

Phospholipase D activity of rat brain neuronal nuclei, measured with e xogenous phosphatidylcholine as substrate, was characterized. The meas ured activity of neuronal nuclei was at least 36-fold greater than the activity in glia nuclei. The pH optimum was 6.5, and unsaturated but not saturated fatty acids stimulated the enzyme. The optimal concentra tion of sodium oleate for stimulation of the enzyme activity was 1.2 m M in the presence of 0.75 mM phosphatidylcholine. This phospholipase D activity was cation independent. In the absence of NaF, used as a pho sphatidic acid phosphatase inhibitor, the principal product was diglyc eride; whereas in the presence of NaF, the principal product was phosp hatidic acid. The phospholipase D, in addition to having hydrolytic ac tivity, was able to catalyze a transphosphatidylation reaction. Maximu m phosphatidylethanol formation was seen with 0.2-0.3 M ethanol. GTP g amma S, ATP gamma S, BeF2, AIF(3), phosphatidic acid, and phosphatidyl ethanol inhibited the neuronal nuclei phospholipase D activity. The ad dition of the cytosolic fraction of brain, liver, kidney, spleen, and heart to the incubation mixtures resulted in inhibition of the phospho lipase D activity. Phospholipase D activity was detectable in nuclei p repared from rat kidney, spleen, heart, and liver.