Tryptophan-specific transfer ribonucleic acid isoacceptors of Escherichia coli exist in active and inactive states as determined by their ability to charge tryptophan under mediation of tryptophanyl transfer ribonucleic acid synthetase. The corresponding tryptophanyl transfer ribonucleic acids also exist in active and inactive states, as determined by their ability to undergo enzymatic discharging of tryptophan. The active and inactive tryptophanyl transfer ribonucleic acids differ in conformation, being separable on columns of hydroxylapatite and of methylated albumin kieselguhr. The conformation of tryptophan transfer ribonucleic acid probably differs from both forms of tryptophanyl transfer ribonucleic acid. Tryptophanyl transfer ribonucleic acids can be converted largely into active or inactive states, remaining in those states under mild conditions even after removal of the converting agent as long as the tryptophanyl residue remains attached, whereas active and inactive tryptophan transfer ribonucleic acids under the same conditions are not stable. Chloroquine converts inactive tryptophan transfer ribonucleic acids into active tryptophan transfer ribonucleic acids, thereby enhancing the rate and extent of charging tryptophan to tryptophan transfer ribonucleic acid by tryptophanyl transfer ribonucleic acid synthetase. Chloroquine also converts inactive tryptophanyl transfer ribonucleic acids into active tryptophanyl transfer ribonucleic acids.
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