Adenylate definition

In fact, kinetic studies of the GTP-dependent avian mitochondrial enzyme indicate two metal-binding sites, one on the polyphosphate group of the bound GTP and one on carboxylate side chains of the protein.252 255 The three-dimensional structure of the ATP-dependent E. coli enzyme reveals a nucleotide binding site similar to the ATP site of adenylate kinase (Fig. 12-30).256 A definite binding site for C02 is also present in the enzyme.257... 

The above-described data show that CRF added to cells of the rat Intermediate lobe In culture causes a rapid stimulation of oe-MSH release and cyclic AMP accumulation, thus demonstrating a direct action of the peptide on pars intermedia cells (15). It is however difficult, using intact cells, to dissociate between increases in cyclic AMP levels due to stimulation of adenylate cyclase activity or to Inhibition of cyclic nucleotide phosphodiesterase or to a combination of both effects. Definitive proof of the role of adenylate cyclase In the action of CRF In the intermediate lobe of the pituitary gland is provided by the following findings of a CRF-lnduced stimulation of adenylate cyclase activity in homogenate of rat and bovine pars Intermedia cells. 

As in the case of adenylate cyclase, the application of chiral phosphate and thiophosphate analysis techniques has yielded the most definitive evidence on the enzymic mechanism of cAMP phosphodiesterase. Eckstein and coworkers were able to determine the stereochemistry of the reaction of cAMP phosphodiesterase from beef heart using the phosphorothioate cAMP(S) substrate (Burgers et al., 1979b). This approach had been made possible by the development of the diastereomers of cAMP(S) by Stec (Baraniak et al., 1979). Phosphodiesterase-catalysed hydrolysis was carried... 

The fourth question takes us close to the core of the problem of the mechanism of protein s3uithesis, and if we knew the answer unequivocally, we could really say we knew something about the way proteins are made in vivo. Unfortunately, we do not have this information, and hence we do not know how far our knowledge of the isolated system applies. All we can say at the present time is that in mammalian systems the sRNA seems to be labeled in a manner sufficiently rapid to be consistent with a precursor role 186). The time scale employed may, however, be much too long to warrant any definitive deductions, and, furthermore, it has not been shown in vivo that the RNA is unlabeled as rapidly as it is labeled, which must be the case if it were an obligatory intermediate. Since the adenylate pathway has been studied so far only in relation to amino acid incorporation in the microsomal system in vitro, and not in relation to net protein synthesis, the ultimate answer to this question is, moreover, intimately tied to solvii the problem of the exact relationship between amino acid incorporation and protein synthesis. This will be discussed in the next section. 

---