Properties of guinea pig liver peroxisomal dihydroxyacetone phosphate acyltransferase.

On subcellular fractionation, the enzyme acyl-CoA: dihydroxyacetone-phosphate 0-acyltransferase (EC 2.3.1.42)in guinea pig liver sediments mainly with the light mitochondrial (L) fraction.From several lines of evidence, it was concluded that this acyltransferase is mainly localized in peroxisomes (microbodies).The properties of the dihydroxyacetone-P acyltransferase present in the L fraction are studied in detail and compared with those of the glycerol-P acyltransferase present in the same fraction.The pH optimum of dihydroxyacetone-P acyltransferase in the absence of detergent is pH 5.5 with activity up to pH 9.0.In the presence of cholate or other detergent, the pH optimum shifts to pH 7.4, with stimulation of enzyme activity.The membrane-bound enzyme is resistant to heat and trypsin treatment, but the enzyme is labile to heat and trypsin in the presence of sodium cholate.The enzyme is not inhibited by high concentrations of N-ethylmaleimide.Cholate, deoxycholate, and Triton X-100 solubilized a portion of the membrane-bound enzyme.The properties of glycerol-P acyltransferase with respect to pH optimum, stability towards detergents, heat, trypsin and N-ethylmaleimide are quite different than those of dihydroxyacetone-P acyltransferase, indicating that these acyltransferases in the L fraction are not the same enzyme.Part of the dihydroxyacetone-P acyltransferase activity is latent, as shown by stimulation upon treatment with detergents, osmotic shock, or son- ication.Kinetic studies with increasing concentrations of dihydroxyacetone-P show a biphasic reciprocal plot at both pH 5.6 and 7.4 (K, 0.06 m~ and 0.25 m~ at pH 5.5 and 0.04 IUM and 0.2 m~ at pH 7.4) with V,, about 10 nmol/min/mg of protein at pH 5.5 and 3.3 m o l / min/mg of protein at pH 7.4.Acyl dihydroxyacetone-phosphate (acyl-DHAP) is an important intermediate in the formation of glycerolipids containing ester and ether bonds (1-3).This lipid was discovered as a rapidly labeled compound formed from 32Pi or [Y-~*P]ATP in guinea pig liver crude mitochondrial fraction (4-6).Later, acyl-DHAP' was shown to be biosynthesized by enzymatic acylation of DHAP with long chain acyl coenzyme A in guinea pig liver mitochondrial and microsomal fractions (7).DHAP acyltransferase (EC 2.3.1.42)has been shown to be widely distributed and is present in the mitochondrial and micro-