cyp11A1 Canola plants under short time heat stress conditions

In order to investigate the high temperature tolerance of spring canola plants (Brassica napus L.) constitutively expressing cyp11A1 gene which encodes bovine cytochrome P450_SCC the growth features were analyzed under short time heat stress (42°C) in growth chamber. Earlier it was documented that results of the heat tolerance test positively correlated with improvement of high temperature resistance in field trial. Higher relative water content (by 13%) and superoxide dismutase (SOD) activity, lower electrolyte leakage (up 1.4-fold) and smaller increase in chlorophyll a and carotenoid contents in cyp11A1 canola leaves in comparison with wild-type plants under stress allowed to conclude cyp11A1 plants are more tolerant to high temperature than the control ones. We suppose that SOD activity increase which revealed in our transgenic canola in normal condition plays the defining role in the biochemical alterations in plant metabolism for the thermotolerance improvement. SOD activity increment could be caused by heterologous cytochrome P450_SCC activity which resulted in the superoxide radical formation. Cyp11A1 canola plants might be resistant to the other stress conditions of different origin.     

Isolation and properties of cortisol inducible and cortisol non-inducible isoenzymes of rat liver tyrosine aminotransferase]

Rat liver contains two groups of tyrosine aminotransferase (TAT) isoenzymes; during electrophoresis in agar gel one of the groups moves to the anode and the other--to the catode. Cortisol is shown to induce only the anode isoenzymes of TAT, which were isolated, purified and thoroughly analyzed. The inducible anode isoenzyme of TAT spearated from other proteins is more sensitive to the effect of proteases (trypsin and chymotrypsin) than the catode isoenzyme. Some kinetic parameters of the purified TAT isoenzymes were studied. Both isoenzymes have pH optimum around 7.5; their apparent Km values for tyrosine are also similar. However, the catode isoenzyme of TAT possesses a higher affinity for alpha-ketoglutarate than does the anode isoenzyme. Unlike the latter, the former isoenzyme may use oxaloacetate as an amino group acceptor. Pyridoxal phosphate is firmly bound to the catode isoenzyme and can be readily spearated from the anode isoenzyme during dyalisis. An increased sensitivity of the inducible isoenzyme to proteases is due not only to the possibility of coenzyme dissociation, but also to some specific properties of the apoenzyme. The results obtained support the assumption that a high sensitivity of the inducible isoenzymes to proteases provides for a removal of excessive amounts of the enzymes from the cells under cessation of hormonal induction, thus maintaining enzymatic homostasis in the cell.