Development and Localization of Carboxypeptidase Activity in Embryo-less Barley Half-kernels

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Abstract
Distal half-kernels of barley (Hordeum vulgare L.), after imbibition for 1 day, produced a carboxypeptidase that was active on N-carbobenzoxy-L-phenylalanyl-L-alanine and on N-carbobenzoxy-L-phenylalanyl-L-phenylalanine. For the ensuing 2 days, activity increased linearly and thereafter increased at reduced rates. Electrofocusing of an imbibed half-kernel homogenate produced coincident peaks of activity on both substrates. Experiments with dissected imbibed (3 days) half-kernels showed that the enzyme arose in the aleurone layer. Enzyme production was inhibited by 6-methylpurine, cordycepin, cyclohexhimide and p-fluorophenylalanine, and activity was inhibited by phenylmethylsulfonylfluoride. The enzyme did not hydrolyze endopeptidase substrates over a range of pH. GA accelerated the rate of release from the aleurone, but was not essential for release and did not appreciably affect the ultimate amount of carboxypeptidase produced. In these respects, the carboxypeptidaase appears to be unique among the known hydrolases produced by barley aleurone tissue.