Lacey J C, Hawkins A F, Thomas R D, Watkins C L
Department of Biochemistry, University of Alabama, Birmingham 35294.
Proc Natl Acad Sci U S A. 1988 Jul;85(14):4996-5000. doi: 10.1073/pnas.85.14.4996.
Amino acids esterified to the ribose group of 5'-adenylic acid (AMP) constantly migrate between the 2' and 3' positions of the ribose at a rate of several times per second, which is slower than the rate of peptide-bond synthesis (15-20 per sec). Because the contemporary protein-synthesizing system only incorporates amino acids into protein when they are at the 3' position of the AMP at the terminus of tRNA, the value of the equilibrium constant relative to the 2' and 3' positions is of considerable interest. Differences between D and L isomers in this regard might be especially revealing. We have used N-acetylaminoacyl esters of AMP as models for the 3' terminus of tRNA and find that glycine and the L amino acids consistently distribute predominantly to the 3' position (approximately equal to 67% 3', approximately equal to 33% 2'), but D amino acids distribute to that position generally to a lesser extent and in a manner inversely related to the hydrophobicity of the amino acid side chain. This consistency of the L amino acid preference for the 3' position, combined with the inconsistency of the D amino acid preference, may be one reason for the origin of our contemporary protein-synthesizing system, which forms the peptide bond preferentially with L amino acids and only when they are in the 3' position of the ribose moiety of the AMP residue at the 3' terminus of every tRNA.
酯化到5'-腺苷酸（AMP）核糖基团上的氨基酸以每秒几次的速率在核糖的2'和3'位置之间不断迁移，这比肽键合成的速率（每秒15 - 20次）要慢。因为当代蛋白质合成系统仅在氨基酸处于tRNA末端AMP的3'位置时才将其掺入蛋白质中，所以相对于2'和3'位置的平衡常数的值备受关注。在这方面，D型和L型异构体之间的差异可能特别具有启发性。我们使用AMP的N - 乙酰氨基酰酯作为tRNA 3'末端的模型，发现甘氨酸和L型氨基酸始终主要分布在3'位置（约67%在3'位，约33%在2'位），但D型氨基酸在该位置的分布通常较少，且与氨基酸侧链的疏水性呈负相关。L型氨基酸对3'位置的这种一致性偏好，与D型氨基酸偏好的不一致性相结合，可能是我们当代蛋白质合成系统起源的一个原因，该系统优先与L型氨基酸形成肽键，且仅当它们处于每个tRNA 3'末端AMP残基核糖部分的3'位置时才会如此。
