β-oxidation and associated enzyme activities in microbodies from germinating peas

The two β-oxidation sites in pea cotyledons : Carnitine palmitoyltransferase: location and function in pea mitochondria

Two sites for β-oxidation of fatty acids in pea (Pisum sativum L.) cotyledons exist. One site is the microbody, the other the mitochondrion. Mitochondrial β-oxidation of fatty acids is carnitine-dependent. The fatty acid permeates the membrane as palmitoylcarnitine which is formed from cytosolic-side palmitoyl-CoA by a carnitine palmitoyltransferase located on the exterior face of the inner mitochondrial membrane as a peripheral protein. A single-gated pore integral membrane translocator is proposed to exchange the palmitoylcarnitine for carnitine or acetylcarnitine across the membrane. An internal (matrix side) carnitine palmitoyltransferase then reforms palmitoyl-CoA which enters β-oxidation and subsequently the tricarboxylic-acid cycle.

The dual location of β-oxidation enzymes in germinating pea cotyledons

β-Oxidation enzymes were detected both in the mitochondria and microbodies of pea cotyledons. Intact mitochondria did not show β-oxidation enzyme activity but in ruptured mitochondria this activity was high. It is apparent that the mitochondrial membrane barrier prevents rapid access of acyl-CoA substrates to matrix β-oxidation sites. Removal of the membrane barrier permits rapid access of acyl-CoAs and these enzyme activities may then be measured.