各种因子对固定化烟草核酮糖1,5-二磷酸羧化酶/加氧酶解离作用的影响

pH,温度、离子强度及效应剂等对固定化烟草RuBP羧化酶在2.5mol/L尿素处理下的解离作用有各种不同的影响。在pH6.0时,仅小亚基从大亚基核(L_8)解离,当pH为中性偏碱时,大亚基核也解离。低温和低离子强度均促进酶的解离,而温度和离子强度对大亚基之间的解离的影响显著大于对大、小亚基之间的影响。这表明酶的亚基之间存在着不同的极性和疏水作用,而大亚基之间的疏水作用比大、小亚基之间的强。6-PG对大、小亚基之间解离的抑制作用表明大亚基上的催化位置与小亚基之间有一定的密切关系。

Effects of Various Factors on the Dissociation of Immobilized Ribulose-1, 5-Bisphosphate Carboxylase/Oxygenase

There were various effects of pH, temperature, ionic strength and effectors on the dissociation of immobilized RubisCO treated with 2.5 mol/L urea. Small subunits were dissociated from the large subunit core (L8) at pH 6.0 while the latter was still bound to the matrix. However, when pH was increased to mildly alkaline, the large subunit core bound to matrix was dissociated into monomer. The amount of dissociated subunits from the immobilized enzyme was proportional to the loss of RubisCO activity (Figs. 1, 2). The intensity of maximum fluorescence emission of the immobilized RubisCO in which part of small subunits was removed decreased slightly, and the wavelength was blue shifted from 341 nm to 336 nm. When the large subunits were dissociated (Fig. 3), the intensity of maximum fluorescence emission decreased greatly. It is suggested that polar interaction between the large and small subunits is different from that between the large subunits.The dissociation of enzyme molecule treated with urea at various pH was accelerated by low temperature (Figs. 4, 5) and ionic strength (Table 1), and the effects of temperature and ionic strength on the dissociation between the large subunits were greater than those on that between the large and small subunits. The results indicate that there is a hydrophobic interaction between the subunits of enzyme, and the hydrophobic bonds between the large subunits are stronger than that between the large and small subunitsGlycerol inhibited the dissociation of large subunits and had almost no effects on the dissociation between the large and small subunits (Fig. 7). 6-PG, which could bind to the catalytic site on the large subunit, greatly inhibited the dissociation between the large and small subunits (Fig. 8). It indicates that there is a certain close interaction between the catalytic site and the small subunit.