Nucleotide hydrolysis, coupling with proteins

A substantial number of observations have demonstrated that the stress-70 proteins bind denatured proteins, as well as some short peptides, and that ATP hydrolysis (possibly with concomitant release of Pj or ADP) results in the release of bound peptides (de Silva et ai, 1990 Hendershot, 1990 Hurtley 1989 Kassenbrock 1988 Palleros etai, 1991). Conversely, bindingof peptides to stress-70 proteins induces ATPase activity above basal levels peptide-induced ATPase activity is often used as a facile in vitro assay for stress-70 protein activity. Schematically, this activity can be subdivided into (1) ATP binding and hydrolysis, followed by product release (P and ADP), (2) peptide binding and release, and (3) a mechanism of coupling peptide binding/release and nucleotide hydrolysis/product release. 

There is considerable evidence that opioid receptors are coupled to G-proteins and produce their effects through these proteins (see Refs. 96, 97 for reviews of opioid receptors and G-proteins). The structure of cloned opioid receptors is consistent with their belonging to this receptor superfamily (see below). G-pro-teins are heterotrimers, consisting of a, jS, and y subunits, which bind guanine nucleotides to their a-subunit and catalyze the hydrolysis of GTP to GDP. G-proteins mediate the interac-... 

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