pH Dependence of the RNase T1 Action on Nucleoside 2', 3'-Cyclic Phosphates

概要

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1) The pH dependence of RNase T1 [EC 2. 7. 7. 26] action on various nucleoside 2', 3'-cyclic phosphates was studied. 2) Optimum pHs for the hydrolysis of guanosine 2', 3'-cyclic phosphate, inosine 2', 3'-cyclic phosphate and xanthosine 2', 3'-cyclic phosphate by RNase T, were 7.0-7.2, 5.5-6.5 and 4.5-5.5 respectively. 3) The cleavage of 3'-xanthylyl bonds in deaminated RNA by RNase T1 was much faster at pH 5.0 than at pH 7.5, the optimum pH for RNA digestion by the enzyme. 4) The difference between the optimum pH for the cleavage of 3'-xanthylyl bond and that of 3'-guanylyl bond was discussed, especially in relation to the pKa values of the lactate form at the 1, 6-position of the purine bases. 5) Thioguanosine 2', 3'-cyclic phosphate and thioinosine 2', 3'-cyclic phosphate were quite resistant to RNase T1 in pH 4-8.
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