Choi Y S, Cho Y D
Department of Biochemistry, College of Science, Yousei University Seoul, Korea.
Biochim Biophys Acta. 1994 Dec 15;1201(3):466-72. doi: 10.1016/0304-4165(94)90078-7.
A new active S-adenosylmethionine decarboxylase (EC 4.1.1.50) (SAMDC II) was extracted from soybean (Glycine max) axes. The enzyme was purified to homogeneity by ammonium sulfate fractionation, DEAE-Sepharose and methylglyoxalbis(guanylhydrazone) (MGBG)-Sepharose 6B chromatographies. The molecular weight of the native enzyme was 110,000, while the subunit molecular weights were 66,000 and 58,000, indicating a heterodimeric structure. The Km value of the enzyme for S-adenosylmethionine was 16 microM, which is two times higher than that of previously reported S-adenosylmethionine decarboxylase (SAMDC I) (8.1 microM). The specific activity of SAMDC II during the seed growth increased rapidly and reached its maximum on the second day after germination whereas that of SAMDC I reached its peak on the fourth day. MGBG was shown to inhibit SAMDC II competitively like SAMDC I. Carbonyl and sulfhydryl group specific reagents modified SAMDC II, resulting in the loss of enzymatic activity. Agmatine, the product of arginine decarboxylation catalyzed by arginine decarboxylase, inhibited the SAMDC II competitively (Ki = 40 microM) while it inhibited the SAMDC II non-competitively (Ki = 600 mM). The possible role of the chronological appearance of SAMDC II and SAMDC I, and properties of the enzyme are briefly discussed in connection with polyamine biosynthesis in soybean axes.
从大豆（Glycine max）胚轴中提取出一种新的活性S-腺苷甲硫氨酸脱羧酶（EC 4.1.1.50）（SAMDC II）。通过硫酸铵分级沉淀、DEAE-琼脂糖和甲基乙二醛双（脒基腙）（MGBG）-琼脂糖6B色谱法将该酶纯化至同质。天然酶的分子量为110,000，而亚基分子量为66,000和58,000，表明其为异二聚体结构。该酶对S-腺苷甲硫氨酸的Km值为16 microM，是先前报道的S-腺苷甲硫氨酸脱羧酶（SAMDC I）（8.1 microM）的两倍。SAMDC II在种子生长期间的比活性迅速增加，并在发芽后第二天达到最大值，而SAMDC I在第四天达到峰值。结果表明，MGBG与SAMDC I一样竞争性抑制SAMDC II。羰基和巯基特异性试剂修饰SAMDC II，导致酶活性丧失。精氨酸脱羧酶催化精氨酸脱羧产生的胍丁胺竞争性抑制SAMDC II（Ki = 40 microM），而非竞争性抑制SAMDC I（Ki = 600 mM）。结合大豆胚轴中的多胺生物合成，简要讨论了SAMDC II和SAMDC I按时间顺序出现的可能作用以及该酶的特性。
