Cell-free extracts of a rhizobacterial isolate from Festuca octoflora Walt. contained a soluble α-ketoglutarate-dependent L-tryptophan (L-TRP) transaminase which catalyzes the conversion of L-TRP to indole-3-pyruvic acid (IPyA). The enzyme was purified 35-fold with protamine sulfate and ammonium sulfate (45-65%) precipitation. The IPyA released in the reaction mixture was trapped and partially stabilized as an enol-borate-arsenate complex and measured spectrophotometrically. IPyA production was directly proportional with time (up to 120min) and protein concentration in the ranges employed. The optimum pH and temperature for the catalytic conversion was pH 8.0 and 40°C, respectively. Using L-TRP as the substrate in the presence of α-ketoglutarate (as an amino-group acceptor) and pyridoxal phosphate (as a coenzyme), the average Kmwas 1.22 mM and the activation energy 21.0 kJ mol-1. The role of this enzyme in the microbial synthesis of auxins and its possible influence on plant growth and development are discussed. © 1988.
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