Catalytic Characteristics of Polyamine Oxidase from Cowpea Primary Leaves
HE Sheng-Gen * HUANG Xue-Lin FU Jia-Rui (The School of Life Sciences, Zhongshan University, Guangzhou 510275, P.R.China)
The catalytic characteristics of a polyamine oxidase (EC 184.108.40.206) purified from the primary leaves of 6-day-old cowpea (Vigna unguiculata) seedlings were studied. The effective substrates of the enzyme were aliphatic diamines such as 1,4-diaminobutane (putrescine, Put), 1,5-diaminopentane (cadaverine, Cad), 1,6-diaminohexane and 1,10-diaminodecane, and the 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 was higher than 2 mmol/L, and that of Spd or Spm was higher than 3 mmol/L. The maximum 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 activity was affected by the ionic strength of the reaction medium. Pre-incubation of the enzyme with K +, Ca 2+ or Mg 2+ at a concentration of 10 mmol/L had no effect on the activity, while Mn 2+, Zn 2+, Fe 2+, Co 2+, and Cd 2+ at the same concentration inhibited the enzyme activity to different extents. The enzyme activity was inhibited by nearly 80% by the metal chelator EDTA (10 mmol/L) or methylglyoxyal-bis (guanylhydrazone) (0.1 mmol/L), a powerful inhibitor of S-adenosylmethionine decarboxylase. Cu-binding inhibitor KCN (1.0 mmol/L) and carbonyl group reagents (hydroxyamine or aminoguanidine, 0.1 mmol/L) led to the complete loss of the activity.