PHYSICOCHEMICAL PROPERTIES OF CHICKPEA LIPOXYGENASES

Purified lipoxygenase isoenzymes from chickpea (Cicer arietinum) cv Pedroxillano are single polypeptide chains with M(r)s of 96000-97000, determined by hydrodynamic and electrophoretic methods. Both isoenzymes differed in pI, 4.92 for CL-1 and 4.74 for CL-2. Each isoenzyme contained one atom of iron in a divalent oxidation state. CL-1 contained 760 amino acid residues and CL-2 753 residues, with a high proportion of hydrophobic amino acids, particularly proline and leucine. Eight and seven cysteines were also present, two and three of which were as free sulphydryl residues, in CL-1 and CL-2, respectively. Thiols, sulphur bridges and carboxyl and amine groups seemed to be essential in the maintenance of a catalytically active tertiary structure in both isoenzymes. CL-2 formed mainly 13-hydroperoxy-(9Z,11E)-octadecadienoic acid from linoleic acid, while CL-1 yielded almost equal proportions of the 9- and 13-hydroperoxides, and the 9- and 13-ketodienes.