Effect of SO32- [sulphite ion] on the activity of ribulose biphosphate carboxylase from seedlings of Pinus silvestris [Pine, sulphite inhibition, Spinacia oleracea, spinach, bicarbonate ion]

• Published in: Physiologia plantarum Vol. 49; no. 4
• Main Authors: Gezelius, K, Haellgren, J.-E. (Umeaa Univ. (Sweden). Dept. of Plant Physiology)
• Format: Journal Article
• Language: English
• Published: 01.08.1980
• ISSN: 0031-9317; 1399-3054

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 deg. C. 1 mM and higher concentrations of SO2/3-inhibited the enzyme. The enzyme was activated either in the assay medium (2.5-20 mM HCO(-/3), 20 mM MgCl(,2)) or in 10 or 20 mM HCO(-/3) and 20-25 mM MgCl(,2). Linear reciprocal plots of the activity versus the substrate concentration were obtained, when the HCO(-/3) concentration during activation was 4 mM or higher. When the enzyme was activated at high HCO(-/3) and Mg('2+) concentrations, the K(, m)(CO(,2)) was c. 27 muM. With respect to HCO(-/3), SO(2-/3) inhibited the enzyme in a non-competitive fashion. The inhibition was similar, whether SO(2-/3) was present during activation or not. Apparently, SO(2-/3) did not interfere with the binding of CO(,2) and Mg('2+) at the activating site. The K(, i) was 11-13 mM SO(2-/3). With respect to ribulose bisphosphate the inhibition was also non-competitive. Similar results with respect to HCO(-/3) were obtained for spinach, Spinacia oleracea L., which is contrary to earlier reports.