Reaction of nitric oxide with synthetic hemoprotein, human serum albumin incorporating tetraphenylporphinatoiron(II) derivatives.
The reaction of nitric oxide (NO) with a synthetic hemoprotein, the recombinant human serum albumin (rHSA) incorporating eight tetraphenylporphinatoiron(II) derivatives bearing a covalently linked axial base (FeP) [rHSA-FeP], has been investigated. The UV--vis absorption spectrum of the phosphate buffer solution (pH 7.3) of rHSA-FeP showed maxima at 425 and 546 nm upon the addition of NO. The carbonyl rHSA-FeP, in which FePs are six-coordinate CO-adducts, also moved to the same species after bubbling with NO gas. ESR spectroscopy revealed that the incorporated FePs in the albumin formed six-coordinate nitrosyl complexes; the proximal imidazole moiety does not dissociate from the central iron when NO binds to the trans side. The NO-binding affinity of rHSA-FeP (P(1/2)(NO), 1.7 x 10(-6) Torr, pH 7.3, 298 K) was significantly lower than that of FeP itself (P(1/2)(NO), 1.8 x 10(-8) Torr in toluene). Kinetically, this arises from the decreased association rate constant (k(on)(NO), 8.9 x 10(8) M(-1) s(-1) --> 1.5 x 10(7) M(-1) s(-1)). Since NO-association is diffusion controlled, incorporation of the synthetic heme into the albumin matrix appears to restrict the NO access to the central iron(II).
Komatsu
T
T
Department of Polymer Chemistry, Advanced Research Institute for Science & Engineering, Waseda University, Tokyo 169-8555, Japan.
Matsukawa
Y
Y
Tsuchida
E
E
D004578:Electron Spin Resonance Spectroscopy; D006420:Hemeproteins / Q000737:chemistry*; D006801:Humans; D007700:Kinetics; D008665:Metalloporphyrins / Q000737:chemistry*; D009569:Nitric Oxide / Q000737:chemistry*; D009603:Nitroso Compounds / Q000737:chemistry; D011994:Recombinant Proteins / Q000737:chemistry; D012709:Serum Albumin / Q000737:chemistry*; D012996:Solutions; D013056:Spectrophotometry, Ultraviolet
D006420:Hemeproteins; D008665:Metalloporphyrins; D009603:Nitroso Compounds; D011994:Recombinant Proteins; D012709:Serum Albumin; D012996:Solutions; C032547:iron tetraphenylporphyrin; D009569:Nitric Oxide