MEMBRANE-ASSOCIATED N-MYRISTOYLTRANSFERASE ACTIVITY IS REDUCED IN OBESE (FA FA) ZUCKER RAT-LIVER

N-Myristoyltransferase is the enzyme that catalyses the transfer of myristate from myristoyl-CoA to the NH2-terminal glycine residue of a number of protein of diverse functions. Many of the known myristoylated proteins are important in signal transduction. We have compared the activity of rat liver N-myristoyltransferase from lean and obese (fa/fa) Zucker rat (a model for non-insulin dependent diabetes mellitus, NIDDM). N-myristoyltransferase activity isolated from the particulate fraction of obese (fa/fa) Zucker rat liver was ~4.7-fold lower than the corresponding activity observed in either the controls or the vanadate-treated obese rat livers. This pattern was only observed in the particulate fraction; the homogenate and soluble N-myristoyltransferase activities were not significantly different to the control activities. N-myristoyltransferase activity isolated from the brain of the four groups showed no significant variations. These results, and previous work [King, M.J., Pugazhenthi, S. Khandelwal, R.L. and Sharma, R.K. (1993) Biochem. Biophys. Acta. 1165, 259-262], would indicate that the rat liver particulate N-myristoyltransferase activity appears to be inversely proportional to the level of plasma insulin, implicating insulin in the control of N-myristoylation. The specific activity of the particulate liver N-myristoyltransferase was approximately 10-fold higher than that of the soluble liver N-myristoyltransferase, raising the possibility that N-myristoyltransferase exists in 2 populations, with the active form of N-myristoyltransferase residing in the membranous fraction. This situation could provide a system whereby N-myristoylation is regulated by the translocation of N-myristoyltransferase from the cytosol to its active site in the membranes. © 1993 Academic Press, Inc.