부산대학교 도서관

The effect of sulphite on ribulose bisphosphate carboxylase, extracted from needles of Pinus silvestris L. was studied in vitro at pH 8.15 and 25°C. 1 mM and higher concentrations of SO32- inhibited the enzyme. The enzyme was activated either in the assay medium (2.5-20 mM HCO3- 20 mM MgCl2) or in 10 or 20 mM HCO3- and 20-25 mM MgCl2. Linear reciprocal plots of the activity versus the substrate concentration were obtained, when the HCO3- concentration during activation was 4 mM or higher. When the enzyme was activated at high HCO3- and Mg2+ concentrations, the Km(CO2) was c. 27 μM. With respect to HCO3-, SO32- inhibited the enzyme in a non-competitive fashion. The inhibition was similar, whether SO32- was present during activation or not. Apparently, SO32- did not interfere with the binding of CO2 and Mg2+ at the activating site. The Ki was 11-13 mM SO32-. With respect to ribulose bisphosphate the inhibition was also noncompetitive. Similar results with respect to HCO3- were obtained for spinach, Spinacia oleracea L., which is contrary to earlier reports. [ABSTRACT FROM AUTHOR]