不同核质组合水稻核酮糖-1,5-二磷酸羧化酶/加氧酶动力学特性

RELATIONSHIP BETWEEN THE NUCLEO-CYTOPLASM COMPOSITION AND THE KINETIC PROPERTIES OF RIBULOSE1,5-BISPHOSPHATE CARBOXYLASE/OXYGENASE OF RICE

用遗传手段获得同质异核,异质同核的水稻(Oryzo satiue L.),提取大亚基(LS)相同、而小亚基(SS)不同和 LS 不同,但 SS 相同的核酮糖-1,5-二磷酸羧化酶/加氧酶(RubisCO),在相同条件下分别测定其 RubisCO 的动力学特性,同质异核水稻间的 RubisCO 的 K_m(O_2)(K。)差异显著,V_(m z)(O_2)(V。)/K。值变化也较大,V_(m z)(CO_2)(V_c)、K_c、V_oV_oK_o/V_oK_o差异不显著。细胞质不同,细胞核相同时,RubisCO 的 K。和 V_cK_o/V_oK_c 值差异显著,K_c 和 V_o 值也变化较大。具有异源细胞质的 RubisCO 比相应的同源 RubisCO 有较高的 RubisC 活性和羧化/加氧比。核质组合对水稻 RubisCO 动力学特性的影响程度依具体核、质组合的不同而异。

Ribulose-l,5-bisphosphate earboxylase/oxygenase (RubisCO, EC 4.1.1.39) was purified from leaves of rice (Oryza sativa), including four fer,ile cultivars and six male-sterile nuclear substi- Tution lines: genome of cultivars in O. saliva L. f. spontanea cytoplasm and in O. sativa subsp indica cv. Gambiaka Kokum cytoplasm, respectively. These RubisCO enzymes were divided into two categories: (a) RubisCO with identical large subunits but different small subuinirs, (b) R.a- bisCO with variable large subunits and identical small subunits. Specific activities for both the carboxylation and oxygenation reactions of RubisCO were determined under standard conditions of activation. It was found that the V_amx,(CO_2) remained constant, but K_m(O_2) changed greatly, ranging from 223 μmol/L to 371 μmol/L in (a) group. The small subunits had significant effec on K,(O_2) and on V_max,(O_s)/K_m(O_2). No significant variation in K_m(CO_2), V_max(O_2), and the specificky factor were detected among the RubisCO with varied small subunits. Significant varia- tion in K_m(O_2) and specificity factor were detected among the enzymes with varied large subunits, which also showed an important effect on K_m(CO_2) and V_max,(O_2). RubisCO with heterologous large subunits had higher carboxylase activity and specificity factor than those with homologous