IDENTIFICATION AND PARTIAL-PURIFICATION OF AN ENDOGENOUS INHIBITOR OFSOLUBLE GUANYLYL CYCLASE FROM BOVINE LUNG

An endogenous inhibitor of soluble guanylyl cyclase from bovine lung h as been partially purified by use of anion exchange, hydrophobic inter action, and gel filtration chromatography. This inhibitor is a protein with a molecular weight of about 149,000 which was estimated from its elution behavior, versus that of a series of standards, on a Sephacry l S-300-HR column. Its activity was measured by comparison of the leve l of cGMP production from soluble guanylyl cyclase in the presence and absence of the inhibitor protein. Soluble guanylyl cyclase is inhibit ed by this protein when either Mg2+ or Mn2+ is used as a cofactor. The insensitivity of its inhibitory activity to both isobutylmethylxanthi ne and the presence of cGMP demonstrates that this new protein is not a phosphodiesterase. This new protein inhibits both activated and unac tivated soluble guanylyl cyclase. Because the inhibition was found to be noncompetitive with respect to the substrate, GTP, it appears that this inhibitor may be an allosteric regulator of soluble guanylyl cycl ase.