GA3-Modulated multiple forms of monophenolase in wheat seed

Multiple forms of monophenolase in wheat half-seeds were separated by molecular sieving on Sephadex G-200. A single molecular form of monophenolase was observed in control, while two multiple forms were present in GA₃-treated wheat half-seeds. A high MW (200 000 or above) multiple form (activity peak I) which eluted soon after the void volume was exclusively present in GA₃-treated half-seeds. The second activity peak (peak II) was a low MW (45 000) multiple form and its elution profile coincided in control and GA₃-treated wheat half-seeds. Both the multiple forms of monophenolase in GA₃-treated wheat half-seeds showed a pH optimum at 9.0, while the optimum enzyme activity of the control molecular form (peak II) was at pH 7.0. This indicated that the treatment of wheat half-seeds with GA₃ brought about a structural modification in monophenolase. The in vitro addition of trypsin enhanced the control of the molecular form of monophenolase but this treatment failed to alter the activity of multiple forms in GA₃-treated half-seeds. This differential response of monophenolase towards trypsin could be ascribed to a conformational change of the enzyme in hormone-treated half-seeds. Brief exposure of the enzyme preparation to urea (6 M) brought about an irreversible activation of monophenolase both in control and GA₃-treated wheat half-seeds.