Stearic acid desaturase activity was assayed in preparations from perigenital adipose tissue and liver from lean and genetically obese female mice (ob/ob). The total activity in the perigenital adipose tissue from obese mice was threefold greater than in the tissue from lean mice, but per g of adipose tissue the activity was twofold greater in tissue from lean mice. In liver, the activity in obese mice was elevated at 8 weeks of age, remained elevated up to 24 weeks and then decreased by half at 48 weeks, but at all ages was higher than that in lean mice. The decrease in desaturase activity of liver from obese mice at 48 weeks corresponded to a change in the fatty acid composition of liver lipids toward that found in lean mice. Whereas in adipose tissue much of the increased enzyme activity may be due to tissue hyperplasia, in liver it is mainly an increased activity per cell.
