Both N-p-coumaroyl- and N-feruloyltyramine accumulated in response to wounding in leaf segments of maize. The amount of N-hydroxycinnamoyltyramines started to increase 3-6 h after wounding and peaked at 12 h. Thereafter, the amount of N-p-coumaroyltyramine decreased rapidly, while the N-feruloyltyramine content remained at a high level. The accumulation of N-hydroxycinnamoyltyramines was accompanied by an increase in the tyramine N-hydroxycinnamoyltransferase (THT) activity. This increase was initially detected 3 h after wounding and reached a maximum at 36 h, the level of activity being 40 and 11 times that in the leaves before wounding and in the control leaves, respectively. Partial purification of THT from wounded leaves by (NH4)2SO4 precipitation and subsequent two steps of anion-exchange chromatography resulted in a 12.5-fold increase in specific activity. Kinetic studies with this partially purified enzyme revealed that the best substrates were tyramine and feruloyl-CoA, although tryptamine and sinapoyl-CoA also efficiently served as substrates. The apparent native molecular weight of the enzyme was determined by gel filtration as 40 kDa.
玉米叶片受伤后,N-对香豆酰基和 N-阿魏酰基
酪胺都会积累。受伤后 3-6 小时,N-羟基肉桂酰基
酪胺的含量开始增加,12 小时达到峰值。此后,N-对香豆酰基
酪胺的含量迅速下降,而 N-阿魏酰基
酪胺的含量则保持在较高
水平。伴随着 N-羟基肉桂酰基
酪胺的积累,
酪胺 N-羟基肉桂酰基转移酶(
THT)的活性也在增加。这种增加最初是在受伤 3 小时后发现的,并在 36 小时后达到最大值,其活性
水平分别是受伤前叶片和对照叶片的 40 倍和 11 倍。通过(NH4)2SO4 沉淀和随后的两步阴离子交换色谱法对受伤叶片中的
THT 进行部分纯化后,比活性提高了 12.5 倍。对这种部分纯化的酶进行的动力学研究表明,最佳底物是
酪胺和阿魏酰-CoA,尽管
色胺和
山奈酰-CoA 也能有效地作为底物。经凝胶过滤测定,该酶的表观原生分子量为 40 kDa。