Thyroidal synthesis of phosphatidic acid.

Abstract

The enzymatic formation of phosphatidic acid from l-α-glycerophosphate and fatty acid was studied in cell free systems of calf and guinea pig thyroid. Phosphatidic acid formation was assayed by measuring the conversion of water-soluble l-α-glycerophosphate to the lipid which is extractable by organic solvents. Palmitate or endogenous fatty acids could serve as cosubstrate in the presence of coenzyme A (CoA) and adenosine triphosphate (ATP). Palmityl-CoA served as cosubstrate in the absence of CoA or ATP. The synthetic system was found in highest concentration in the particulate fraction of ruptured thyroid cells which sedimented between 8500 and 100,000 ×g. The system has a pH optimum of 7.5, has an absolute Mg requirement, is not inhibited by Ca, and does not require sulfhydryl groups (aside from reduced CoA). This system is essentially similar to that known to exist in liver and involves 2 enzymes: the first, acyl-CoA synthetase, forms the CoA derivative of long chain fatty acids in the presence of ATP,...