Open AccessEvidence for the Presence of Two Kinetically Distinct Active Forms of Ribonuclease T 2
Author(s) -
YASUDA Toshihiro,
INOUE Yasuo
Publication year - 1981
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1111/j.1432-1033.1981.tb05140.x
Subject(s) - chemistry , protonation , carboxylate , substrate (aquarium) , cationic polymerization , rnase p , catalysis , reaction rate constant , medicinal chemistry , stereochemistry , uridine , ribonuclease , computational chemistry , ion , kinetics , organic chemistry , rna , biochemistry , biology , ecology , physics , gene , quantum mechanics
A kinetic study has been made of the RNase‐T 2 ‐catalyzed transphosphorylation of two adenine nucleotides, adenylyl(3′‐5′)uridine and adenosine 3′‐(1‐naphthyl)phosphate. Rates were measured at pH values ranging from 2.6 to 8.2. The observed shape of the plot of log k cat against pH for both the natural and the synthetic substrate suggests that there exist two parallel rate‐determining pathways. Two pH‐independent rate constants and three ionization constants of the enzyme‐substrate complexes were obtained by nonlinear iterative least‐squares analysis. Detailed interpretation of the pH profiles was carried out and it is proposed that carboxylate anion is likely to deprotonate O‐2′ at 4 < pH < 6, but at pH > 6 an alternative general base would play this role more effectively than the carboxylate group. Another base in its protonated cationic form is responsible for the general acid catalysis.