. The biosynthesis of proteins. Proteins -- Synthesis. CHEMICAL PATHWAYS 99 change of ATP concentration is observed (De Moss et al., 1956), and no free aminoacyl adenylate could ever be detected (Hoagland et al., 1956). Using large amounts of pure tryptophan activation enzyme, Kingdon et al. (1958) and Karasek et al. (1958) were able to liberate tryptophanyl adenylate by denaturing the enzyme. The amount of anhydride obtained is com- patible with the existence of one molecule of tryptophanyl adenylate per molecule of enzyme. The aminoacyl adenylate might therefore be described as a prosthetic
. The biosynthesis of proteins. Proteins -- Synthesis. CHEMICAL PATHWAYS 99 change of ATP concentration is observed (De Moss et al., 1956), and no free aminoacyl adenylate could ever be detected (Hoagland et al., 1956). Using large amounts of pure tryptophan activation enzyme, Kingdon et al. (1958) and Karasek et al. (1958) were able to liberate tryptophanyl adenylate by denaturing the enzyme. The amount of anhydride obtained is com- patible with the existence of one molecule of tryptophanyl adenylate per molecule of enzyme. The aminoacyl adenylate might therefore be described as a prosthetic group of the enzyme, rather than as a substrate or reaction product. Actually, free aminoacyl adenylates would rapidly disappear in the cell and be wasted in all kinds of reactions; it is quite certain that their being bound to the activation enzyme protects them from reacting at random (Askonas et ah, 1957; Moldave et al., 1959). They are anhydrides of a carboxylic acid with adenylic acid, and belong therefore to the class of mixed anhydrides of a carboxylic acid with a phosphoric group which carries a substituent. Substances of this type have been shown to be rather. OH OH Fig. 27. Amino acyl adenylate. Stable in water, and much more so than the corresponding compound with unsubstituted phosphoric group like acetylphosphate (Chantrenne, 1948). On the other hand, they react very rapidly with amino acids to form a pep- tide bond, even in 10"^ M solution at pH 74 and this is a purely non-enzymic reaction (Chantrenne, 1947, 1948, 1949, 1950; Katchalski and Paecht, 1954; Avison, 1955; Moldave et al, 1959). Free aminoacyl adenylates in neutral or slightly alkaline medium would rapidly form polypeptides at random or produce a large variety of peptides by reacting with any amino acid present. The formation of well-defined proteins from such substances is possible only if they are in some way prevented from reacting at random (Chantrenne, 1950). That their binding to the enzyme p
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