Coenzyme A in purified peroxisomes is not freely soluble in the matrix but firmly bound to a matrix protein.

On subfractionation of purified rat liver peroxisomes in matrical, peripheral membrane, integral membrane and core protein fractions, the endogenous peroxisomal CoA was released together with the matrix proteins. The released CoA could not be measured by an enzymatic cycling assay unless the matrix proteins were denatured by acid treatment or by heating at alkaline pH. The cofactor could not be removed by dialysis of the matrix proteins unless salt was added. It was not displaced by exogenous CoA. It migrated into sucrose density gradients together with a protein of approximately 80 kDa. The results indicate that peroxisomal CoA is firmly bound to a matrix protein and that the presence of CoA inside purified peroxisomes does not necessarily imply that the peroxisomal membrane is impermeable to this cofactor.