RESUMO
A homogenous preparation of putrescine synthase, the versatile multifunctional enzyme involved in agmatine→putrescine conversion in Cucumis sativus was found to catalyze enzymatic decarboxylation of arginine also. Similarly, the purified arginine decarboxylase mediated the component as well as the complete set of coupled reactions harboured by putrescine synthase. Both the enzyme preparations exhibited identical electrophoretic and chromatographic behaviour and were immunologically indistinguishable. All the enzymic activities are stabilized concurrently by feeding arginine to the intact seedlings. Therefore, it is concluded that the multifunctional putrescine synthase in Cucumis sativus seedlings also harbours arginine decarboxylase activity unlike its counterpart in Lathyrus sativus.
RESUMO
The multifunctional enzyme, putrescine synthase has been purified from Cucumis sativus and characterized. This enzyme harbours agmatine iminohydrolase, ornithine transcarbamylase, putrescine transcarbamylase and carbamate kinase activities, whose concerted action results in agmatine → putrescine conversion. The enzyme resolved into two aggregation forms, enzyme aggregated and enzyme monomer upon electrophoresis at pH 8·3. Evidence has been provided by two-dimensional gel electrophoresis that both enzyme aggregated and enzyme monomer comprise of identical polypeptide chains. Under non-reducing conditions on sodium dodecyl sulphate-polyacrylamide gel electrophoresis, the protein moves as a single 150 KDa polypeptide; however, in the presence of 2-mercaptoethanol on sodium dodecyl sulphate-polyacrylamide gel elec trophoresis, it migrates as 3 polypeptides of molecular weight 48,000, 44,000 and 15,000. The enzyme undergoes age-dependent in vivo proteolytic degradation from a 66 KDa polypeptide (primary translational product), through 48 KDa polypeptide to 44 KDa species and finally to small molecular weight peptides.