MUTATION OF HIS-105 IN THE BETA(1)-SUBUNIT YIELDS A NITRIC OXIDE-INSENSITIVE FORM OF SOLUBLE GUANYLYL CYCLASE

Soluble guanylyl cyclase [GTP pyrophosphate-lyase (cyclizing); EC 4.6. 1.2] is a hemoprotein that exists as a heterodimer; the heme moiety ha s been proposed to bind nitric oxide, resulting in a dramatic activati on of the enzyme. Mutation of six conserved His residues reduced but d id not abolish nitric oxide stimulation whereas a change of His-105 to Phe in the beta1 subunit yielded a heterodimer that retained basal cy clase activity but failed to respond to nitric oxide. Heme was not det ected as a component of the mutant heterodimer and protophorphyrin IX failed to stimulate enzyme activity. The activity of the His mutant wa s almost identical to that of the wild-type enzyme in the presence of KCN, suggesting that disruption of heme binding is the principal effec t of the mutation. Thus, the mutation provides a means to inhibit the nitric oxide-sensitive guanylyl cyclase signaling pathway.