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Tri acyl glycerol synthesis in isolated fat cells evidence that the sn glycerol 3 phosphate acyl transferase ec 2.3.1.15 and di hydroxy acetone phosphate acyl transferase ec 2.3.1.42 activities are dual catalytic functions of a single microsomal enzyme


Journal of Biological Chemistry 251(18): 5738-5744
Tri acyl glycerol synthesis in isolated fat cells evidence that the sn glycerol 3 phosphate acyl transferase ec 2.3.1.15 and di hydroxy acetone phosphate acyl transferase ec 2.3.1.42 activities are dual catalytic functions of a single microsomal enzyme
The acyl-CoA[Coenzyme A]:-sn-glycerol-3-phosphate acyltransferase (EC 2.3.1.15) (glycerol-P acyltransferase) and acyl-CoA:dihydroxyacetone phosphate acyltransferase (EC 2.3.1.42) (DHAP acyltransferase) activities were investigated in vitro in order to evaluate the quantitative contribution of the glycerol-P and DHAP pathways for the synthesis of triacylglycerols in isolated fat cells [rat] and to test the hypothesis that these 2 activities may be dual catalytic functions of a single enzyme. More than 85% of both acyltransferase activities was associated with the microsomal subcellular fraction. The microsomal glycerol-P acyltransference activity showed an apparent Km of 8 .mu.M for glycerol-P with a Vmax of 15.6 nmol/min per mg, while the DHAP acyltransferase activity showed an apparent Km of 40 .mu.M for DHAP with a Vmax of 9.7 nmol/min per mg. Glycerol-P was a competitive inhibitor (Ki = 7.2 .mu.M) of the DHAP acyltransferase, and DHAP was a competitive inhibitor (Ki = 92 .mu.M) of the glycerol-P acyltransferase. The 2 acyltransferase activities showed virtual identity in their pH dependence, acyl-CoA chain length dependence, thermolability and inactivation by N-ethylmaleimide. Trypsin, detergents, collagenase, phospholipases and various salts and organic solvents also had similar effects on both activities. The microsomal glycerol-P and DHAP acyltransferase activities probably actually represent dual functions of a single enzyme. Calculations based on the above kinetic constants and previously reported glycerol-P and DHAP pools in adipocytes suggest that the in vivo ratio of glycerol-P to DHAP acylation should be greater than 24:1.


Accession: 006839854



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