Comparative specificity of plasma lecithin:cholesterol acyltransferase from ten animal species.

The molecular specificities of plasma lecithin:cholesterol acyltransferase (LCAT) from ten animal species have been compared. Using a reassembled high density lipoprotein containing a mixture of phosphatidylcholines, the relative rates of liberation of different species of cholesteryl ester were measured. All but two species of LCAT clustered according to one of three patterns of substrate specificity. The LCAT from six species, including human, did not transfer highly polyunsaturated fatty acyl chains. In addition, human LCAT transesterified saturated fatty acyl chains more effectively than unsaturated fatty acyl chains. We conclude that the structures of the active sites of the enzymes differ, and that this may be related to size constraints that prevent efficient binding of large bulky phosphatidylcholines.