水稻叶片蔗糖磷酸合成酶的一些特性

水稻叶片粗提液经硫酸铰分部沉淀、DE 52纤维素及 Sephadex G—200柱层析,得到较纯的蔗糖磷酸合成酶。该酶的最适 PH约7.0;UTP,UDP,ATP能明显地抑制其酶活;UTP是该酶UDPG的竞争性抑制剂,Mg~( )对它有促进作用;G6P则无影响。酶的两个底物F6P及UDPG的饱和动力学曲线分别为双曲线型和S型;K_m(F6P)=0.93 mmol/L;K_m(UDPG)=20.0 mmol/L;V_m(F6P)=83.3 nmol Suc mg~(-1)Protein min~(-1);V_m(UDPG)=333 nmol Suc mg~(-1)protein min~(-1);Hill(F6P)=1.0,Hill(UDPG)=1.4。水稻叶片蔗糖磷酸合成酶的活性受 ATP,UTP,UDP,UDPG等因素的调节。水稻叶片中蔗糖合成酶的总活力大于或等于蔗糖磷酸合成酶。

Some Properties of Rice Leaf Sucrose Phosphate Synthetase

Sucrose phosphate synthetase (EC 2.4.1.14)is one of the key enzymes in sucrose metabolism.The activity of SPS directly affects the partitionof photosynthetic products, such as statch andsucrose. The higher activity of this enzyme,the more the sucrose accumulates in leaves.The activity of SPS can be regulated by some fac-tors. We have partially purified SPS from rice lea-ves by ammonium sulfate fractionation, DEAE-cellulose (DE52) chromatography (Fig. 1) andSephadex G--200 chromatography (Fig. 2). Theoptimum pH of SPS is about 7.0. UTP UDP andATP can strongly inhibit its activity. UTP is acompetitive inhibitor with UDPG. Mg~( ) canstimulate SPS activity. G6P has no effect. Thelower concentration of Pi has no apparent effect.I_(0.5) (Pi) is about 40 mmol/L (Fig. 3). Saturationkinctic curves of two substrates F6P and UDPGare hyperbolic (Fig. 5) and sigmoid (Fig. 6),respectively. Thc kinetic coefficientS are K_m(F6P)=0.93 mmol/L; Km (UDPG) = 20mmol/L; Vm(F6P) =83.3 nmol Suc, mg~(-1) Protein min~(-1); Vm(UDPG) =333 nmol Suc mg~(-1) Protein min~(-1);Hill (F6P) =1.0; Hill (UDPG) =1.4. Theexperiment concludes that the rice leaf SPS is aregulatory enzyme. The activity of SPS can beregulated by UTP, UDP, ATP, UDPG and otherfactors. The total activity of SS from ricc leafis equal to or higher than that of SPS.