Acyl adenylates and

According to this proposal, the incorporation of proline into collagen follows the acyl adenylate and acyl RNA stages now generally believed to occur in protein synthesis. A bound hydroxyproline intermediate is postulated, from which hydroxyproline is transferred to soluble RNA. We prefer to suggest that different RNA acceptor molecules exist for hydroxyproline and proline this would be consistent with recent work which indicates that the soluble RNA molecule contains the information for incorporation of a particular amino acid into protein (3). Although it is conceivable that there is hydroxylation of prolyl-sRNA to yield hydroxyprolyl-sRNA, an additional mechanism would be needed... 

Although ubiquitin has not been found in prokaryotes, ubiquitin s molecular ancestors were recently identified in prokaryotes. Remarkably, these proteins take part not in protein modification but in biosynthesis of the coenzyme thiamine (p. 423). A key enzyme in thiamine biosynthesis is ThiF, which activates the protein ThiS as an acyl adenylate and then adds a sulfide ion derived from cysteine (Figure 23.9). ThiF is homologous to human Ft, which includes two tandem regions of 160 amino acids that arc 28% identical in amino acid sequence with a region of ThiF from E. coli. 

Organic chemists activate carboxylic acids by converting them into acyl halides or acid anhydrides. Cells activate carboxylic acids by converting them into acyl phosphates, acyl pyrophosphates, acyl adenylates, and thioesters. 

Describe the reaction that links coenzyme A (CoA) to a fatty acid. Explain the roles of the acyl adenylate and inorganic pyrophosphatase (PPiase) in the reaction. 

Characteristic feature of the peptide synthetase systems is that the activation reaction of each amino acid substrate, i.e. amino acyl adenylate and thioester... 

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