Karpel R L, Merkler D J, Flowers B K, Delahunty M D
Biochim Biophys Acta. 1981 Jun 26;654(1):42-51. doi: 10.1016/0005-2787(81)90134-9.
Under conditions of low ionic strength, ribonuclease A, which binds more tightly to single- than to double-stranded DNA, lowers the melting temperature of DNA helices (Jensen and von Hippel (1976) J. Biol. Chem. 251, 7198-7214). The effects of chemical modification of lysine and arginine residues on the helix-destabilizing properties of this protein have been examined. Removal of the positive charge on the lysine epsilon-amino group, either by maleylation or acetylation, destroys the ability of RNAase A to lower the Tm of poly[d(A-T)]. However, reductive alkylation of these residues, which has not effect on charge, yields derivatives which lower the Tm by only about one-half that seen with unmodified controls. Phenylglyoxalation of arginines can largely remove the Tm-depressing activity of RNAase A. RNAase S, which is produced by cleavage of RNAase A between amino acids 20 and 21, possesses DNA helix-destabilizing activity comparable to that of the parent protein, whereas S-protein (residues 21-124) increases poly[d(A-T)] Tm and S-peptide (1-20) has no effect on Tm. These results suggest that specific location of several basic amino acids situated on the surface of RNAase A is largely responsible for this protein's DNA melting activity.
在低离子强度条件下，与单链DNA结合比与双链DNA结合更紧密的核糖核酸酶A会降低DNA螺旋的解链温度（詹森和冯·希佩尔（1976年）《生物化学杂志》251卷，7198 - 7214页）。已经研究了赖氨酸和精氨酸残基的化学修饰对该蛋白质螺旋去稳定特性的影响。通过马来酰化或乙酰化去除赖氨酸ε-氨基上的正电荷，会破坏核糖核酸酶A降低聚[d(A - T)]解链温度的能力。然而，这些残基的还原烷基化对电荷没有影响，产生的衍生物降低解链温度的程度仅约为未修饰对照的一半。精氨酸的苯乙二醛化可在很大程度上去除核糖核酸酶A的解链温度降低活性。核糖核酸酶S是由核糖核酸酶A在氨基酸20和21之间切割产生的，其具有与亲本蛋白质相当的DNA螺旋去稳定活性，而S蛋白（残基21 - 124）会提高聚[d(A - T)]的解链温度，S肽（1 - 20）对解链温度没有影响。这些结果表明，位于核糖核酸酶A表面的几个碱性氨基酸的特定位置在很大程度上决定了该蛋白质的DNA解链活性。
