Abstract
Recent studies on the enzymic mechanisms of protein synthesis have emphasized the importance of the “activation” of the cu-carboxyl groups of amino acids, i.e. the conversion of the amino acids into reactive acylating agents. The work of numerous investigators (for a recent review, see Chantrenne (1)) has suggested that this activation process, which requires the participation of adenosine 5’-triphosphate, involves the formation of a-aminoacyladenylates, which are thought to be the reactive amino acid derivatives in the biosynthesis of proteins from free amino acids. In view of the present state of our knowledge, it is desirable to consider the possible role, in protein synthesis, of other low molecular weight derivatives of amino acids. In previous publications from this laboratory (2, 3), it was reported that intracellular proteolytic enzymes catalyze transamidation reactions of the type,
Highlights
Preparation and Properties of Carbobenzoxyglycyl-L-tyrosyladenylate-The synthetic procedure was similar to that described for carbobenzoxy-L-tyrosyladenylate, except that 1.44 mmoles of adenosine 5’-monophosphate and of carbobenzoxyglycyl-n-tyrosine (m.p., 106-108” [16]) were coupled in the presence of 1.5 moles of the carbodiimide
Were suspended in 20 ml. of cold methanol containing 8 to 10 mmoles of glacial acetic acid per mmole of adenylate, and the hydrogenolysis was conducted at O-4”, in the presence of freshly prepared spongy palladium catalyst
Other Compounds-W-labeled glycyl+ctyrosine was prepared from uniformly labeled Myrosine via the carbobenzoxydipeptide; specific radioactivity, 18,000 c.p.m. per pmole
Summary
N-tyrosinamide is incubated with the mitochondrial fraction, the mixed proteins become labeled, and the extent of labeling increases with the time of incubation. The procedure developed involves the reaction of carbobenzoxy-n-tyrosine (or of carbobenzoxyglycyl-L-tyrosine) with adenosine 5’-monophosphate in the presence of a slight excess of N ,N’-dicyclohexylcarbodiimide, followed by catalytic hydrogenolysis of the coupling product. When the mitochondrial fraction of rat liver homogenates was incubated with CY-tyrosyladenylate, the proteins were found to be labeled (Table I); this “incorporation” does not appear to be enzymic in nature, since prior heat treatment of the mitochondrial fraction does not abolish the labeling, as in the case of the amide, but instead markedly enhances it.
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