Biochemistry of Suberization: omega-Hydroxyacid Oxidation in Enzyme Preparations from Suberizing Potato Tuber Disks

Abstract

A cell-free extract obtained from suberizing potato (Solanum tuberosum L.) tuber disks catalyzed the conversion of 16-hydroxy[G-(3)H]hexadecanoic acid to the corresponding dicarboxylic acid with NADP or NAD as the cofactor, with a slight preference for the former. This omega-hydroxyacid dehydrogenase activity, located largely in the 100,000g supernatant fraction, has a pH optimum of 9.5. It showed an apparent Km of 50 muM for 16-hydroxyhexadecanoic acid. The dehydrogenase activity was inhibited by thiol reagents, such as p-chloromercuribenzoate, N-ethylmaleimide, and iodoacetamide, and this dehydrogenase is shown to be different from alcohol dehydrogenase. That 16-oxohexadecanoic acid was an intermediate in the conversion of 16-hydroxyhexadecanoic acid to the corresponding dicarboxylic acid was suggested by the observation that the cell-free extract also catalyzed the conversion of 16-oxohexadecanoic acid to the dicarboxylic acid, with NADP as the preferred cofactor. The time course of development of the omega-hydroxyacid dehydrogenase activity in the suberizing potato disks correlated with the rate of deposition of suberin. Experiments with actinomycin D and cycloheximide suggested that the transcriptional processes, which are directly related to suberin biosynthesis and omega-hydroxyacid dehydrogenase biosynthesis, occurred between 72 and 96 hours after wounding. These results strongly suggest that a wound-induced omega-hydroxyacid dehydrogenase is involved in suberin biosynthesis in potato disks.