Evidence for a factor in pig adipose tissue controlling the specificity of the acyltransferase(s) of triacylglycerol synthesis.

The proportion of palmitate at position 2 of triacylglycerols synthesized by microsome-cytosol preparations of rat, mouse, or chicken adipose tissue was found to be markedly increased by the addition of an inactivated preparation of pig adipose tissue microsomes. A phosphate extract of pig adipose tissue microsomes was also active in directing palmitate to position 2 of rat triacylglycerols. The proportion of palmitate at position 2 of triacylglycerols synthesized was reduced by prior repeated extraction of the pig adipose tissue microsomes with phosphate. The pretreatment specificity was restored when the extract was added back to the microsomes. These observations support the proposal that the unusually high proportion of palmitate at position 2 of lard results from the action of a factor controlling the specificity of the acyltransferase(s) from pig adipose tissue.