The catalytic characteristics of a polyamine o xidase (EC 1.4.3.6) purified from the primary leaves of 6-day-old cowpea (Vi gna unguiculata) seedlings were studied. The effective substrates of the enzym e were aliphatic diamines such as 1,4-diaminobutane (putrescine, Put), 1,5-dia minopentane (cadaverine, Cad), 1,6-diaminohexane and 1,10-diaminodecane, and t he catalytic activity decreased with an increase in the carbon chain length. The enzyme also showed a significant activity towards spermidine (Spd) and spermine (Spm). Substrate inhibition was observed when the concentration of Put or Cad w as higher than 2 mmol/L, and that of Spd or Spm was higher than 3 mmol/L. The ma ximum activity of the enzyme was observed at pH 7.0 for both Put and Cad as the substrates, while that for Spd or Spm was found to be 6.5. The enzyme activi ty was affected by the ionic strength of the reaction medium. Pre-incubation of the enzyme with K+, Ca2+ or Mg2+ at a concentration of 10 mmol/L had no effect on the activity, while Mn2+, Zn2+, Fe2+, Co2 +, and Cd2+ at the same concentration inhibited the enzyme activity to d ifferent extents. The enzyme activity was inhibited by nearly 80% by the metal c helator EDTA (10 mmol/L) or methylglyoxyal-bis (guanylhydrazone) (0.1 mmol/ L), a powerful inhibitor of S-adenosylmethionine decarboxylase. Cu-binding inh ibitor KCN (1.0 mmol/L) and carbonyl group reagents (hydroxyamine or aminoguanid ine, 0.1 mmol/L) led to the complete loss of the activity.%从豇豆幼苗(6 d苗龄)初生叶提纯得到的多胺氧化酶(EC 1.4.3.6)属于二胺氧化酶,最有效的底物是1,4-二胺丁烷( 腐胺)、1,5-二胺戊烷(尸胺)、1,6-二胺己烷、1,10-二胺癸烷等α-二胺,其催化活性随二胺类底物碳链的增长而相应减弱.豇豆多胺氧化酶对亚精胺和精胺也具有较高的催化活性.另外,底物腐胺和尸胺的浓度超过2 mmol/L或亚精胺和精胺浓度超过3 mmol/L时会对酶活性有抑制效应.以腐胺和尸胺为底物时,酶的最适pH约为7.0,而以亚精胺和精胺为底物时其最适pH为6.5.该酶的催化活性还随反应介质的离子强度增加而降低.K+, Ca 2+ 和Mg2+(皆为10 mmol/L)对酶活性无明显抑制作用,而同样浓度的Mn 2+, Zn2+, Fe2+, Co2+ 和Cd2+ 则对酶活性有不同程度的抑制作用.金属螯合剂EDTA(10 mmol/L)和腺苷蛋氨酸脱羧酶抑制剂甲基乙二醛-双脒腙(0.1 mmol/L)可抑制酶活性约80%,而铜结合剂KCN(1.0 mmol/L)、羰基试剂羟胺(0.1 mmol /L)和氨基胍(0.1 mmol/L)可导致该酶完全失活.
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