ON THE ESTIMATION OF THE CONTRIBUTION OF W-OXIDATION TO OVERALL, FATTY-ACID OXIDATION

w-0xidation of a specifically C-14 labelled fatty acid will often prod uce differently labelled acetyl CoA molecules than will normal R-oxida tion, as well as labelled succinates when the C-14 is on the first 4 o r last 4 carbons. These facts have been previously used in ingenious a pproaches developed by Landau and coworkers to estimate w-oxidation bo th in vivo and in liver tissue. However, newer results have weakened t he bases for some of these approaches. w-oxidation now is considered t o be largely peroxisomal, and the major product of peroxisomal fatty a cid oxidation (B- or w-) is now thought to be acetate. The acetate pro duced in vivo will largely escape, by isotopic exchange, into the circ ulation. Thus approaches based solely on acetyl CoA labelling can grea tly underestimate w-oxidation in vivo. We show that approaches based o n the production of labelled succinate produce the most unambiguous es timations of w-oxidation.