A protein tyrosine kinase associated with the ATP-dependent inactivation of adipose diacylglycerol acyltransferase-1.

Abstract

An enzyme activity that reversibly inactivates adipose glycerolphosphate acyltransferase (GPAT) and diacylglycerol acyltransferase (DGAT), in vitro, in the presence of ATP, has been partially purified from adipose tissue with an apparent molecular weight of 68 kDa. The activity responsible for inactivation DGAT is associated with a kinase activity as determined by phosphate incorporation into microsomes and a tyrosine containing peptide. Major substrates of this kinase are two microsomal polypeptides of 53 and 69 kDa. Both DGAT inactivation and kinase activities assayed from the purified sample and the cytosol, have been found to be insensitive to the Ser/Thr kinase inhibitor H-7 while being sensitive to the inhibitors genistein and tyrphostin 25. A crude protein phosphatase preparation from the liver was capable of reversing the effects of both activities. The purified sample was also shown to inactivate GPAT in the presence of ATP. These results suggest that a protein tyrosine kinase, in concert with a protein tyrosine phosphatase, may regulate the activities of DGAT and GPAT by a phosphorylation-dephoshorylation mechanism.