Specificity of acyl-CoA:phospholipid acyltransferases: solvent and temperature effects.

Acyltransfer from CoA thiol esters to either the 1- or 2-position of monoacylglycerophosphoryl choline, which is catalyzed by a microsomal preparation from rat liver, had a temperature optimum of 30-35 degrees C. No significant alteration was observed in the ability of the acyltransferases to distinguish among the various thiol esters tested in the range of 15-40 degrees C. Acyl-CoA:1-acylglycerophosphoryl choline acyltransferase activity is inhibited by urea, N-alkyl ureas, and short-chain alcohols. The effect is not equal for all acyl derivatives, and ethylene glycol has much less inhibitory effect on the transfer of acids with an n - 6 (omega6) double bond. On the other hand, this inhibition of acyltransfer was relatively insensitive to the configuration of the Delta(9)-double bond of octadecadienoates. The specificity of the enzyme-catalyzed transfer of different acids to the 2-position can be correlated in part with the dissociation constants for the urea clathrate complexes. Added glycol does not appreciably alter the specificity of enzyme-catalyzed transfer to the 1-position, but it inhibits the transfer of all acids in a similar fashion.