燕麦幼苗单胺氧化酶的热稳定性及催化特性研究

含黄素单胺氧化酶(MAO)在生物体内通过对单胺类物质的氧化脱氨作用生成相应的醛、氨气和过氧化氢。MAO在植物中的研究较少,通过对燕麦幼苗MAO的研究发现,暗条件下生长的燕麦幼苗匀浆内所含MAO活性均高于光照条件,且发芽三天左右的幼苗体内MAO的活性达到峰值(2.5pKat/mg),同时测定不同组织中MAO的活性为:幼芽>幼根>种子。对纯化后的燕麦MAO的热稳定性和催化特性研究表明:燕麦MAO的热稳定性较差,常温下易失活,37℃和50℃下水浴90min后,活性损失分别为50%和75%;燕麦MAO对底物的选择性较强,只对低浓度的苄胺和苯乙胺的氧化具有催化效果,Km分别为265μmol/L和705μmol/L;在对底物的特异性方面与人类MAO B有一定的相似性,但体外催化效率低于黑曲霉MAO和人类MAO B。

Study on Thermal Stability and Catalytic Specificity of Monoamine Oxidase in Oat Seedlings

FAD-containing monoamine oxidase(MAO;EC 1.4.3.4) oxidises monoamines to their corresponding aldehydes,H2O2,and NH3 in organism.There are seldom reports about MAOs in plants.MAO activity was detected in oat seedlings during germination using benzylamine as substrate.The activities of oat seedlings growing in dark were higher than in light conditions.The activity,reached a peak after germinated for 3 days,was 2.5pKat/mg.and there are little difference about MAO activity in three parts of seedlings,shoots > roots > grains.The results of thermal stability shown oat MAO was unstable in room temperature after purified to homogenate successfully.50% and 75% of oat MAO activity were lost after the 90-min incubation.Oat MAO shows high substrate specificities for benzylamine and phenethylamine,which are traditional MAO B specific substrates and are oxidised to benzaldehyde and phenylacetaldehde,but not for tyramine,serotonin,histamine or dopamine.The Km values for benzylamine and phenethylamine were 265μM and 705μM,respectively.Catalytic efficiency of oat MAO was lower than human MAO B and Aspergillus niger MAO.