水稻和烟草核酮糖1，5－二磷酸羧化酶／加氧酶大小亚基之间的分子杂交

利用固定化Ｒｕｂｉｓｃｏ大小亚基解离重组技术，进行水稻和烟草Ｒｕｂｉｓｃｏ大小亚基之间的分子杂交，实验表明，无论同源或异源的小亚基重组到固定化的大亚基上去后，其羧化酶活性没有明显的变化，但对加氧酶活性却有明显的影响。当水稻Ｒｕｂｉｓｃｏ的大亚基同烟草小亚基杂交重组后，其加氧酶活性同固定化水稻Ｒｕｂｉｓｃｏ相比有明显的增高，因而其羧化／氧化比值下降，并且接近于对照的固定化烟草Ｒｕｂｉｓｃｏ。反之，当烟草Ｒｕｂｉｓｃｏ的大亚基与水稻小亚基杂交重组后，其加氧酶活性同固定化烟草Ｒｕｂｉｓｃｏ相比有明显降低，因而其羧化／氧化比值升高，并接近于对照的固定化水稻Ｒｕｂｉｓｃｏ。由此推测，高等植物Ｒｕｂｉｓｃｏ的小亚基对酶的羧化／氧化比值有一定的影响。

Molecular Hybridization of Rubisco Subunits Between Rice and Tobacco

Both homogenous and hetero genous molecular hybridizations between large and small subunits were performed after dissociation of immobilized Rubisco from tobacco or rice at 2. 5 mol/L urea. The results showed that homogenous and heterogenous hybidizations led to similar recovery of caboxylase activity, but much different recovery in oxygenase activity (Figs. 1, 2). The oxygenase activity of heterogenous hybrid enzyme between immobilized large subunit from rice and free small subunit from tobacco was found to be higher than that of homogenous recontituted enzyme from rice, so that its ratio of carboxylase to oxygenase was lower than that of homogenous reconstituted enzyme and similar to that of undissociated immobile Rubisco from tobacco(Fig. 4). On the other hand, in the case of the immobilized large subunit from tobacco hybridized with free small subunit from rice, its ratio of carboxylase to oxygenase is higher than that of homogenous reconstituted enzyme due to the red uction of oxygenase activity,and also similar to that of the undissociated immobile Rubisco from rice (Fig. 3 ). Therefore, it is sugsested that the function of RubisO small subunts may be involved in the oxygenase activity (Table 1), which resuts in a change of the carboxylation / oxygenation ratio of Rubisco.