A genuine acyl donor activity of oleyl-CoA for mitochondrial glycerophosphate acyltransferase

Abstract

Both mitochondria and microsomes of mammalian organs contain glycerophosphate acyltransferase (EC 2.3.1.15), the first enzyme in the pathway of glycerolipid biosynthesis from sn-glycerol 3-phosphate [l-4]. The mitochondrial glycerophosphate acyltransferase shows 4-6 times preference for palmityl-CoA over oleyl-CoA as acyl donor. By contrast, the microsomal enzyme is highly active with either acyl-CoA [1,2]. With both mitochondrial and microsomal glycerophosphate acyltransferase, the acylation takes place in position 1 of sn-glycerol 3-phosphate molecule [ 1,5,6]. Thus, the properties of the mitochondrial enzyme provide the basis of an excellent mechanism for the selective positioning of saturated fatty acids in position 1 found in most naturally occurring glycerophospholipids [5,6]. To determine the degree of acyl-CoA specificity of the mitochondrial glycerophosphate acyltransferase, we have tested whether the small amount of activity associated with the mitochondrial fraction in the presence of oleyl-CoA is indeed a mitochondrial property or a reflection of microsomal contamination. With oleyl-CoA as the acyl donor, the mitochondrial acyltransferase was unaffected by N-ethylmaleimide and trypsin and, was stimulated by acetone and polymyxin B. All of these reagents strongly inhibited the microsomal enzyme. These distinguishing properties together with an analysis of the acylation products establish that oleyl-CoA is a true acyl donor for mitochondrial glycerophosphate acyltransferase.