In view of the possible effects of the sphingoid base on protein kinases, and the fact that the sphingoid bases used in previous studies were not chemically well-defined, we have studied the effects of chemically well-defined sphingosines and their derivatives on kinase activity. Both (4E)-D- and (4E)-L-erythro-sphingenine showed a weak inhibitory effect, and (4E)-L-threo-sphingenine had a moderate inhibitory effect. In contrast, (4E)-N,N-dimethyl-D-erythro-sphingenine and the sphingosine preparation from a commercial source showed a strong inhibitory effect on PK-C in A431 cells as well as on purified PK-C. Synthetic (4E)-D-erythro-sphingenine and several samples of natural sphingosine inhibited v-src or c-src tyrosine kinase activity measured with polyglutamate-tyrosine (4:1) as substrate. N-Acetylated or N-methylated sphingosines did not inhibit src kinase activity, but rather produced a consistent 1.5-2-fold stimulation of such activity.
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