SERINE BASE-EXCHANGE ENZYME-ACTIVITY IS MODULATED BY SPHINGOSINE AND OTHER AMPHIPHILIC COMPOUNDS - POSSIBLE ROLE OF POSITIVE CHARGE IN INCREASING THE SYNTHESIS OF PHOSPHATIDYLSERINE

It has been found that sphingosine and sphingosylphosphorylcholine (am phiphilic cations) have a stimulatory, and cholesterol 3-sulfate (an a mphiphilic anion), an inhibitory, effect on [C-14]serine incorporation into phosphatidylserine in glioma C6 and rat liver microsomes. In gli oma intact cells sphingosine stimulates phosphatidylserine synthesis i n a process independent of protein kinase C, but suppressed by thapsig argin. We suggest that the stimulation of the enzyme occurs by the int eraction of amphiphilic cations with the membrane cosubstrate phosphol ipids, leading to a charge redistribution on their phosphate groups, a nd hence facilitating the enzyme action. A new hypothesis concerning t he mechanism of the serine base exchange reaction is discussed. (C) 19 97 Academic Press.