Fatty acid elongation and desaturation in bovine tissues

Abstract

Initially, assay conditions were established for the fatty acid elongation and desaturation pathways of bovine liver and adipose tissue microsomes; rat liver microsomes were used as a reference. Rat liver elongation activity was .503 [plus or minus] .020 nmol*min^-1*mg protein^-1; bovine liver microsomal elongation activity was substantially lower, with a mean value of .148 [plus or minus] .020 nmol*min^-1*mg protein^-1. The elongation activity associated with bovine adipose tissue microsomes (.419 [plus or minus] .102 nmol*min^-1*mg protein^-1, respectively no desaturase activity was observed in bovine liver microsomes. Eight Angus and seven Braford heifers were slaughtered at approximately 12 months of age. Actual and adjusted fat thickness were higher in the Angus cattle as compared to the Braford heifers. There were no differences (P >.05) observed in adipose cell size or cells per gram tissue among the Angus and Braford breeds. Therefore, the increase in subcutaneous adipose tissue was not due to hypertrophy of the adipose cells, but was the result of a greater number of subcutaneous adipocytes in the Angus heifers. Subcutaneous adipose tissue and liver samples were taken from the cattle immediately after slaughter for the elongation and desaturation assays. The elongation rate was approximately five times greater in the adipose tissue in comparison to the liver, whereas all the desaturase activity was observed in the adipose tissue and none was observed in the liver. The inability of liver to desaturate stearate was in agreement with the fatty acid profile data which indicated less oleate and more stearate in liver than in adipose tissue. In comparing the elongation rate to the desaturation rates, it was observed that the desaturation activity was one-third the elongation activity. There were no significant differences found between the Angus and Braford heifers for the elongation or desaturation activities. To conclude, the data suggest that the conversion of palmitate to oleate occurs predominantly in the adipose tissue of cattle and the rate-limiting process may be the addition of the double bond (desaturation) and not the addition of 2 carbons to the fatty acid (elongation).