Liang Z, Yu C, Huang A H
Arch Biochem Biophys. 1984 Sep;233(2):393-401. doi: 10.1016/0003-9861(84)90460-0.
Intact spinach (Spinacia oleracea L.) leaf peroxisomes converted glycerate to serine in the presence of NAD and alanine. The reaction proceeded optimally at pH9. Addition of oxaloacetate or alpha-ketoglutarate plus aspartate enhanced the conversion about three-fold. Alteration of the concentration of one of the reaction components, consisting of 2 mM glycerate, 0.2 mM NAD, 0.5 mM oxaloacetate, and 2 mM alanine, revealed half-saturation constants of 0.45 mM for glycerate, 0.06 mM for NAD, 0.02 mM for oxaloacetate, and 0.33 mM for alanine. The conversion proceeded with the formation of hydroxypyruvate followed by serine; hydroxypyruvate did not accumulate to a high amount in the presence or absence of alanine. The amino group donor could be alanine (half-saturation constant, 0.33 mM), glycine (0.45 mM), or asparagine (0.67 mM); the three amino acids produced roughly similar Vmax values. The results indicate that, in the conversion of glycerate to serine, the transamination is catalyzed by a hydroxypyruvate aminotransferase with characteristics unknown among all other studied leaf peroxisomal aminotransferases. The peroxisomal membrane is sparsely permeable to NAD/NADH, and the participation of the peroxisomal malate dehydrogenase in an electron shuttle system across the membrane in the regeneration of NAD/NADH is suggested.
完整的菠菜（Spinacia oleracea L.）叶片过氧化物酶体在NAD和丙氨酸存在的情况下将甘油酸转化为丝氨酸。该反应在pH9时进行得最为理想。添加草酰乙酸或α-酮戊二酸加天冬氨酸可使转化率提高约三倍。改变由2 mM甘油酸、0.2 mM NAD、0.5 mM草酰乙酸和2 mM丙氨酸组成的反应组分之一的浓度，结果显示甘油酸的半饱和常数为0.45 mM，NAD为0.06 mM，草酰乙酸为0.02 mM，丙氨酸为0.33 mM。该转化过程伴随着羟基丙酮酸的形成，随后生成丝氨酸；无论有无丙氨酸存在，羟基丙酮酸都不会大量积累。氨基供体可以是丙氨酸（半饱和常数为0.33 mM）、甘氨酸（0.45 mM）或天冬酰胺（0.67 mM）；这三种氨基酸产生的最大反应速度值大致相似。结果表明，在甘油酸向丝氨酸的转化过程中，转氨作用由一种羟基丙酮酸氨基转移酶催化，其特性在所有其他已研究的叶片过氧化物酶体氨基转移酶中均未知。过氧化物酶体膜对NAD/NADH的通透性较低，提示过氧化物酶体苹果酸脱氢酶参与了跨膜电子穿梭系统中NAD/NADH的再生过程。
