Identification of genes mediating branched chain fatty acid elongation

: Saturated branched chain fatty acids (BCFA) terminating with either a prop-2-yl (iso) or sec-butan-2-yl (anteiso) group are common bioactive food components consumed from beef, fish, and dairy products. Little is known about the endogenous metabolism of BCFA and the enzymes mediating their interconversions. By using transient transfection studies, we report for the first time the substrate specificity of the elongase of very long chain fatty acids (ELOVL)1-7 toward anteiso-15:0 and iso-18:0, and assessed competition between BCFA and normal saturated fatty acids (n-SFA). ELOVL6 mediates elongation of anteiso-15:0→anteiso-17:0, while ELOVL3 is active toward iso-18:0→iso-20:0. Competition studies reveal n-16:0 competes with anteiso-15:0 for ELOVL6, while n-18:0 competes with iso-18:0 for ELOVL3. These competitions for elongation may have implications in specialized tissues where both BCFA and n-SFA are present at comparable levels.