氨基酸对锯缘青蟹N-乙酰氨基葡萄糖苷酶的效应

Inhibitory Effects of Amino Acids on the β-N-acetyl-D-glucosaminidase from Green Crab(Scylla serrata)

研究Gly、Ala、Val、LeuI、le、Pro、Phe、Met、Asn、Cys、Ser、Thr、Asp、Glu、His、Lys、Arg等17种氨基酸对锯缘青蟹(Scylla serrata)N-乙酰--βD-氨基葡萄糖苷酶(NAGase)活力的影响.结果表明:非极性氨基酸中Gly、Ala、Leu、Phe对酶活力几乎没有作用,而ValI、le对酶略有激活,20 mmol/L的Val可以使酶活力提高7.5%,40 mmol/L的Ile可以使酶活力提高10.5%;Pro、Met对该酶略有抑制作用,当浓度为40 mmol/L时,分别可以使酶活力下降15.2%和9.8%;极性氨基酸Asn、Cys、Ser、Thr对酶的活力没有影响;带负电荷的酸性氨基酸Asp和Glu对酶有抑制作用;带正电荷的碱性氨基酸His对该酶略有抑制,Lys和Arg对该酶抑制作用较强.研究Lys和Arg对酶催化pNP-NAG水解反应的抑制机理,并测定其抑制常数,结果表明:Lys和Arg的抑制作用均表现为可逆效应,抑制类型均为反竞争性抑制,其KIS分别为5.29mmol/L和3.76 mmol/L.

The β-N-acetyl-D-glucosaminidase （NAGase, EC 3.2.1.52） catalyzes the cleavage of N-acetylglucosamine polymers. It is a composition of the chitinases and cooperates with endo-chitinase and exo-chitinase to disintegrate chitin into N-acetylglucosamine. It is widely distributed in animal tissues and in microorganisms. The effects of amino acids on the activity of NAGase from the Green Crab （Scylla serrata） were studied. The results showed that some hydrophobic amino acids （Gly, Ala, Leu, Phe） had no effects on the enzyme activity while Val and lie activated the enzyme activity lightly. When the concentration of Val was 20 mmol/L, the enzyme activity was increased by 7.5 %, and when the concentration of Ile was 40 mmol/L, the enzyme activity was increased by 10.5 %. Pro and Met had lightly inhibitory effects on the enzyme activity. 40 mmol/L of Pro or Met could lead to losing the enzyme activity by 15.2% and 9.8%, respectively. Hydrophilic amino acids （Asn,Cys, Ser,Thr） had no effect on the enzyme activity. The acidic amino acids （Asp and Glu） had inhibitory effects on the enzyme. The alkaline amino acids also inhibited the enzyme,and the inhibitory intensity was the order of Arg〉Lys〉His. The inhibition of Lys or Arc was determined to be reversible reaction with remaining enzyme activity. The inhibitory mechanism belonged to be un-competitive types and their KIS was determined to be 5.29 mmol/L for Lys and 3.76 mmol/L for Arc.