The Effect of Mercaptoethanol on the Activity of Enzymes of Nitrogen Metabolism in Leaves from Urtica dioica and Spinacia oleracea.

The effect of mercaptoethanol at different concentrations on enzyme activity was investigated in leaves from Urtica dioica and Spinacia oleracea. The interference of mercaptoethanol with enzyme activity is dependent on the type of plant. the configuration of the enzyme and the concentration of mercaptoethanol. A stimulation of GDH (glutamate-dehydrogenase) was obtained in both species, while inhibition of GOT (glutamate-oxaloacetate transaminase) and GPT (glutamate-pyruvate transaminase) was demonstrated in Spinacia. The stimulation of GOT and GPT activity in Urtica was probably due to inhibition of phenol oxidase. Conclusions concerning the effect of mercaptoethanol on NR (nitrate reductase) activity were difficult to draw, since mercaptoethanol itself reduced nitrite and interfered with NR determination in tests in vitro. In Urtica, no activity could be obtained at all with the in vitro method, probably because an inhibitor of NR was liberated during the extraction procedure. Activity of NR could however be obtained in both species when using the in vivo method. Addition of protective agents to the extraction medium has been supposed to influence the protein extractability. In conformity with this increasing amount of fresh matter to the same volume of extraction medium resulted in decreased protein extractability. This led to differences in enzyme activity when expressed on a fresh weight basis but the specific activity remained constant. [ABSTRACT FROM AUTHOR]