Characterization of two forms of the multifunctional protein acting in fatty acid beta-oxidation

The enzymatic apparatus of fatty acid beta-oxidation in peroxisomes and glyoxysomes includes a multifunctional protein. Two forms of this protein were detected in extracts from cotyledons of germinating cucumber seeds and separated on hydroxylapatite. The two proteins purified to apparent homogeneity possessed enoyl-CoA hydratase, 3-hydroxyacyl-CoA epimerase, and 3-hydroxyacyl-CoA dehydrogenase activity; the proteins are therefore trifunctional. Analysis of molecular structures and kinetic parameters of the two enzyme forms revealed significant differences in size and amino acid composition. The two proteins were characterized as monomers exhibiting molecular weights of 74,000 and 76,500. Likewise, the data obtained with limited proteolysis proved the occurrence of two independent proteins. Immunological comparisons were performed with antibodies raised against the 76.5-kDa protein. They indicated a weak relationship between the two proteins. From that we conclude that within one type of organelle, i.e., glyoxysome, two isoenzymes with multiple functions are located.