one way to explain all of the results obtained is to view hormonally sensitive adenylyl cyclase systems as two-state enzymes whose activities are regulated by gtp and gdp through an allosteric site related to the catalytic moiety , and receptors as entities that are inactive and hence unable to couple unless occupied by hormones and activated by any guanine nucleotide through a distinct receptor-related process .
C0018340
gdp
C0018328
guanine