title: Activation of soluble guanylyl cyclase by four-coordinate metalloporphyrins: evidence for a role for porphyrin conformation.
abstract: Four-coordinate metalloporphyrins activate soluble guanylyl cyclase. Ni(II)PPIX and Cu(II)PPIX are high affinity activators, with activation constants of 24 and 17 nM, respectively. Both metalloporphyrins remain stably bound to the enzyme, enabling spectroscopic characterization of the Ni(II)- and Cu(II)-reconstituted protein. Electronic absorption and resonance Raman spectroscopy reveal that Ni(II)PPIX remains four coordinate when bound to soluble guanylyl cyclase. Analysis of the vibrational frequencies of the Ni(II)-reconstituted enzyme suggests that the protein imposes a constraining force on the porphyrin, favoring a planar conformation. Spectroscopic data for the Cu(II)-substituted protein are also consistent with four coordination. The intensification of the vibrational modes of the peripheral vinyl groups in both Ni(II)- and Cu(II)-reconstituted soluble guanylyl cyclase are consistent with a substantial influence of the protein on the porphyrin environment. Together these data support a model where activation of soluble guanylyl cyclase correlates with the absence of a metal-to-proximal histidine bond and with decreased conformational freedom for the tetrapyrrole in the activated state.
authors.affiliation: Department of Chemistry, University of Wisconsin-Madison, 1101 University Avenue, Madison, WI 53706, USA.
authors.forename: Heather S
authors.initials: HS
authors.lastname: Carr
authors.forename: Dat
authors.initials: D
authors.lastname: Tran
authors.forename: Mark F
authors.initials: MF
authors.lastname: Reynolds
authors.forename: Judith N
authors.initials: JN
authors.lastname: Burstyn
authors.forename: Thomas G
authors.initials: TG
authors.lastname: Spiro
mesh_terms: D000818:Animals; D002417:Cattle; D004789:Enzyme Activation; D006162:Guanylate Cyclase / Q000378:metabolism*; D008665:Metalloporphyrins / Q000378:metabolism*; D012995:Solubility; D013059:Spectrum Analysis, Raman
chemical_list: D008665:Metalloporphyrins; D006162:Guanylate Cyclase