Copper P L, Power D M, Richards J T, Davies J V
Int J Radiat Biol Relat Stud Phys Chem Med. 1978 Nov;34(5):431-8. doi: 10.1080/09553007814551091.
The radical anions (SCN)2.- and Br2.- produced during a pulse radiolysis of the respective potassium salts have been used to study the tryptophan residues of the glucoenzyme, glucoamylase I (EC 3.2.1.3.). At neutral pH, Br2.- reacted with the tryptophan residues of glucoamylase I as expected from previous studies of proteins and free amino acids. However, (SCN)2.- at neutral and high pH was surprisingly unreactive towards the native enzyme. Reaction did occur, however, between (SCN)2.- and glucoamylase from which one-third of the covalently bound carbohydrate had been removed, producing a tryptophyl radical. Reaction also occured between (SCN)2.- and glucoamylase I inactivated by treatment with sodium dodecyl sulphate, but the tryptophan residues were not involved. It is concluded from the results that two 'types' of tryptophan residues are found in glucoamylase I; both are attacked by Br2.- but only one type is attacked by (SCN)2.-.
在各自钾盐的脉冲辐解过程中产生的自由基阴离子（SCN）₂⁻和Br₂⁻已被用于研究葡糖淀粉酶I（EC 3.2.1.3.）的色氨酸残基。在中性pH值下，Br₂⁻与葡糖淀粉酶I的色氨酸残基发生反应，这与先前对蛋白质和游离氨基酸的研究预期一致。然而，在中性和高pH值下，（SCN）₂⁻对天然酶出奇地没有反应性。不过，（SCN）₂⁻与已去除三分之一共价结合碳水化合物的葡糖淀粉酶之间确实发生了反应，产生了色氨酰自由基。（SCN）₂⁻与经十二烷基硫酸钠处理而失活的葡糖淀粉酶I之间也发生了反应，但色氨酸残基未参与其中。从结果得出结论，在葡糖淀粉酶I中发现了两种“类型”的色氨酸残基；两者都受到Br₂⁻的攻击，但只有一种类型受到（SCN）₂⁻的攻击。
