• KSBB Journal
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• v.11 no.3
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• pp.295-302
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• 1996

The measurements of rubisco parameters are important in photosynthetic studies. In this experiment, we used photometric assay method to detect these major parameters, such as activity, carbamylation and amount of rubisco. The main advantages of this method are very simple and as sensitive as conventional methods which usually produce radioactive waste. In this study, with kidney bean (Phaseolus vulgatis L.) leaves grown at normal $CO_2$ (350ppm) and high $CO_2$ (650 ppm), we investigated the effect of $CO_2$ concentration on activation and carbamylation of rubisco by measuring the rubisco activity, carbamylation rate and amount of rubisco using a dual beam (334nm and 405nm) spectrophotometer, and analyzed the polypeptide profiles of rubisco by SDS-PAGE. When $CO_2$ concentration was raised from 350ppm to 650ppm, all parameters of rubisco were decreased : $41.2{\mu}M/m^2/s and 52.2{\mu}M/m^2/s$ to $27.4{\mu}M/m^2/s and 46.1{\mu}M/m^2/s$ for initial and total rubisco activity, respectively ; from 79% to 58.9% for carbamylation rate ; from $1.94 {\mu}M/m^2$ to 1.58{\mu}M/m^2$ for amount of rubisco. These results suggests that the decrease in rubisco activity at high $CO_2$ was caused by carbamylation. The analysis of the preparation by SDS-PAGE showed two major polypeptides at 50 and 14.5 kD which were identified as the large and the small subunits of rubisco. There were no differences in the intensity compared high $CO_2$ to normal $CO_2$ in both 50 kD and 14.5 kD bands. We also found that these inhibitory effects of $CO_2$ were reversible. When high $CO_2$ was switched to normal $CO_2$, the parameters of rubisco changed were almost the same as normal rubisco parameters. These data provide an evidence that activity of rubisco was recovered by $CO_2$ concentration of 350 ppm.