Abstract:Proline synthesis and accumulation has often been shown to occur in plants as a consequence of environmental stress. The physiological significance of proline accumulation is assumed to be associated with the suggested ability of proline to act as an osmoregulator, protective agent or storage compound. Despite the importance of this compound, however, the exact metabolic route and enzymes involved in the synthesis of proline in plants have not been unequivocally identified. The proline synthesis route in plants is thought to resemble the pathway in bacteria. With the exception of △1-pyrroline-5-carboxylate reductase (P5CR), which has been recently characterized, little is known about the other two enzymes, glutamyl kinase (GK) and γ-glutamyl phosphate reductase (GPR). This present paper provides the preliminary results of GK activity assay and its partial purification in rice (Oryza sativa L. ). The enzyme activity assayed was quite low. Different saturation of (NH4)2SO4 was used for precipitation of sample proteins, the enzyme was enriched in the fraction of 30%--60% (NH4)2SO4 saturation and showed a two-fold increase in the assayed activity. The enzyme activity was inhibited by the addition of proline from 10 to 1000 mmol/L. The result indicated that the enzyme from rice was less sensitive to feedback inhibition by proline than that in bacteria. The enzyme was primarily purified by Sephadex G- 150 chromatography. Two activity peaks were discovered in the fractions.