Mechanism of palmityl coenzyme A inhibition of liver glycogen synthase.

Palmityl-CoA inhibits free liver glycogen synthase; the concentration required for half-maximum inhibition is 3 to 4 micrometer. Almost complete inhibition was observed at 50 micrometer. Palmityl-CoA inhibition is associated with dissociation of the tetrameric enzyme into monomers, and binding of palmityl-CoA to the monomers. Glycogen-bound enzyme is also inhibited by palmityl-CoA, resulting in dissociation of the enzyme into monomers and concomitant release of the enzyme from the primer glycogen. Palmityl-CoA inhibition of the enzyme is partially reversed by the glycogen synthase activator, glucose-6-P, whereas sodium lauryl sulfate-inhibited enzyme is not reactivated by glucose-6-P. Sodium lauryl sulfate inhibition results in the dissociation of the tetramer into the monomers. Bovine serum albumin and cyclodextrin can prevent palmityl-CoA inhibition only when they are added prior to palmityl-CoA addition. The possible physiological role of palmityl-CoA in glucose homeostasis is discussed.