EFFECTS OF ADDED L-CARNITINE, ACETYL-COA AND COA ON PEROXISOMAL BETA-OXIDATION OF [U-C-14]HEXADECANOATE BY ISOLATED PEROXISOMAL FRACTIONS

(1) During peroxisomal beta-oxidation of [U-C-14]hexadecanoate, at con centrations higher than 100 mu M, long-chain 3-oxoacyl-CoA-esters and 3-oxobutyryl-CoA accumulate. Only 3-oxobutyryl-CoA accumulates at a lo w concentration of [U- C-14]hexadecanoate. Accumulation of long chain 3-oxoacyl-CoA esters is most extensive when the supply of CoA can be c onsidered limiting for beta-oxidation. (2) Added acetyl-CoA was found to inhibit peroxisomal beta-oxidation. This inhibition was not signifi cantly relieved by added L-carnitine and carnitine acetyltransferase ( EC 2.3.17). (3) Added L-carnitine, at concentrations below 0.2 mM, was found to stimulate peroxisomal beta-oxidation of [U-C-14]hexadecanoat e by up to 20%, causing the conversion of acetyl-CoA into acetylcarnit ine. Higher concentrations of L-carnitine were progressively inhibitor y to beta-oxidation. This effect was specific for L-carnitine as both D-carnitine and aminocarnitine neither caused stimulation at low conce ntrations, nor inhibition at higher concentrations. Added L-carnitine caused accumulation of acylcarnitines of chain-lengths ranging from 4 to 16 carbon-atoms. The inhibition observed with higher concentrations of added L-carnitine is likely due to conversion of [U-C-14]hexadecan oate into [U-C-14]hexadecanoylcarnitine. (4) Low concentrations of add ed hexadecanoylcarnitine was shown to inhibit peroxisomal beta-oxidati on by about 15%, while added acetylcarnitine did not inhibit at concen trations up to 100 mu M. (5) These data are interpreted to indicate si gnificant control being exerted on flux at the stage of thiolysis eith er directly by means of CoA availability, or indirectly by means of th e rate of acetyl-CoA generation.