β-oxidation enzymes and the carnitine-dependent oxidation of palmitate and palmitoyl CoA in mitochondria from avocado

Two sites for the β-oxidation of fatty acids in avocado (Persea americana L.) mesocarp exist. One site is the microbody, the other the mitochondrion. It is apparent that the mitochondrial membrane barrier, which remains intact after sucrose density gradient centrifugation, prevents rapid access of acyl CoA substrates to matrix β-oxidation sites. Thus, intact mitochondria showed little β-oxidation enzyme activity. Rupturing of the mitochondrial membrane allowed rapid access of the acyl CoA substrates to matrix sites. Consequently, in ruptured mitochondria, high O₂-oxidation enzyme activities were measured. O₂ uptake studies further distinguished the two organellar sites of β-oxidation. During palmitoyl CoA oxidation, O₂ uptake was reduced by catalase and increased by KCN in the microbodies, whilst mitochondrial O₂ uptake was unaffected by catalase and reduced by KCN. This reflected the differing fates of FADH₂, produced during the first β-oxidation step, in the two organelles. In addition, only the mitochondrial β-oxidation of fatty acids was carnitine-dependent.