Section 14
Chapter 13,172

Phenylalanyl-tRNA synthetase from yeast and its discrimination of 19 amino acids in aminoacylation of tRNA (Phe) -C-C-A and tRNA (Phe) -C-C-A (3'NH2)

Freist, W.; Sternbach, H.; Cramer, F.

European Journal of Biochemistry 240(3): 526-531


ISSN/ISBN: 0014-2956
PMID: 8856050
DOI: 10.1111/j.1432-1033.1996.0526h.x
Accession: 013171580

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For discrimination between phenylalanine and 18 other naturally occurring non-cognate amino acids by the class II aminoacyl-tRNA synthetase specific for phenylalanine, discrimination factors, D, of 190-6300 have been determined from kcat and Km values. Generally, phenylalanyl-tRNA synthetase is more specific than the class II enzymes specific for Lys and Thr, but works with lower accuracy than the class I enzymes specific for Ile, Tyr, and Arg. In aminoacylation of tRNA(Phe)-C-C-A(3'NH2) discrimination factors D1 vary between 80 - 1610. Pretransfer proof-reading factors Pi1, are in the range 2.3 - 74, post-transfer proof-reading factors Pi22 in the range 1.0 - 4.6, showing that pre-transfer proof-reading is the main correction step, post-transfer proof-reading is less effective or negligible. Initial discrimination factors (I1 and I2) caused by differences in Gibbs free energies of binding between phenylalanine and non-cognate amino acids have been calculated assuming a two-step binding process. Factors I1 can be related to hydrophobic-interaction forces depending on accessible surface areas of the amino acids, factors I2 scatter about a low mean value and do not show any relation to amino acid structures or surfaces, indicating less checking of amino acid side chains in the putative second binding step.

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