Abstract
Upon exposure to water stress, the specific activity of the key Crassulacean acid metabolism enzyme, phosphoenolpyruvate (PEP) carboxylase, increased several-fold in Sedum rupestre L. Photoperiodic long days were without effect. PEP carboxylase was purified from drought-stressed S. rupestre . The enzyme had an apparent molecular weight of 400,000 and was composed of four 100 kilodalton subunits. It had a Michaelis constant of 200 micromolar for PEP and was inhibited by malate with a Ki of 700 micromolar. During drought stress the apparent affinity for PEP did not change. Monospecific polyclonal antibodies were raised against the purified protein. Immunoblot analysis after different periods of drought stress showed that the increase in PEP carboxylase activity was the result of de novo synthesis of PEP carboxylase protein.
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