[Conformation mobility of the universal acceptor end of tRNA]

The conformation analysis of tRNA acceptor fragment XCCA (X=A) was performed. The ribose conformation was taken rigid C(3')-endo. The optimum conformation was found for the ACCA fragment. It was shown that the omega, omega'-angle of the terminal adenine in any crystal modification of the yeast tRNAFen is not optimal. The conformation mobility of the 3'-end ACCA fragment was calculated in the vicinity of optimum conformation. Redundant energy required for keeping the correct 3'-terminal tRNA orientation about the enzyme catalytic centre during any small orientation distortions of the non-universal X-nucleotide relative to the enzyme was estimated. The distortions may occur when non-gomologous tRNA interact with aminoacyl-tRNA-synthetase. It was found that redundant energy for 3' displacement is very anisotropic and some small X-nucleotide reorientation may decrease the catalitic velocity of aminoacylation u0(4)--10(5) times.