Guanosine nucleotide regulatory

Figure 9.7 Effects of cAMP contributing to relaxation. AC, adenylate cyclase DG, diacyl glycerol G, guanosine nucleotide regulatory protein IP3, Inositol trisphosphate, MLCK, myosin light chain kinase.

The knowledge that cyclic AMP is involved in hormone effects stimulated interest in other cyclic nucleotides. Yet only one of these, cyclic GMP (cyclic guanosine 3, 5 -monophosphate), is known to occur in nature, having been discovered first in rat urine in 1963 [9] and then in all mammalian tissues examined in other organisms and in bacteria, but whether it too plays a regulatory role in cell activity is not known [6J. 

A number of 1 3 C nmr studies on the structure and conformation of nucleotides have been performed in the last few years (Birdsall and Feeney, 1972 Blumenstein and Raftery, 1972, 1973 Tapper et al., 1972, 1973 Lapper and Smith, 1973 Que et al., 1973 Smith et al., 1973a Birdsall et al., 1973a). Guanosine tetraphosphate, a nucleotide which exhibits regulatory control in the interaction of... 

It was observed that the adenine sensitivity of the double mutant could be overcome by adding guanosine to the medium (78). This and other data demonstrated that the double mutant was starved for GMP in the presence of excess AMP. The implication for wild-type cells was that any regulatory mechanisms operating at the IMP branchpoint could be overridden by a high concentration of adenine nucleotides, even under conditions of guanine nucleotide deficiency. 

Regulatory control of bacterial thymidylate synthetases by nucleotides has not been reported however, Lorenson et al. (7) investigated that of the chick embryo thymidylate synthetase and found that the 5 -mono-, di-, and triphosphates of adenosine, cytidine, guanosine, and uridine, and of their deoxyribosides, did not inhibit activity. Thus, the activity of the synthetase, from this source at least, does not seem to be subject to allosteric regulation by nucleotides. With crude extracts of Ehrlich ascites... 

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