Anomalously slow cyanide binding to Glycera dibranchiata monomer methemoglobin component II: Implication for the equilibrium constant

Journal Article · Tue Oct 18 00:00:00 EDT 1988 · Biochemistry; (USA)

DOI:https://doi.org/10.1021/bi00421a011· OSTI ID:7189724

Mintorovitch, J; Satterlee, J D ^[1]

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1. Univ. of New Mexico, Albuquerque (USA)

In comparison to sperm whale metmyoglobin, metleghemoglobin {alpha}, methemoglobins, and heme peroxidases, the purified Glycera dibranchiata monomer methemoglobin component II exhibits anomalously slow cyanide ligation kinetics. For the component II monomer methemoglobin this reaction has been studied under pseudo-first-order conditions at pH 6.0, 7.0, 8.0, and 9.0, employing 100-250-fold mole excesses of potassium cyanide at each pH. The analysis shows that the concentration-independent bimolecular rate constant is small in comparison to those of the other heme proteins. Furthermore, the results show that the dissociation rate is extremely slow. Separation of the bimolecular rate constant into contributions from k{sub CN{sup {minus}}} (the rate constant for CN{sup {minus}} binding) and from k{sub HCN} (the rate constant for HCN binding) shows that the former is approximately 90 times greater. These results indicate that cyanide ligation reactions are not instantaneous for this protein, which is important for those attempting to study the ligand-binding equilibria. From the results presented here the authors estimate that the actual equilibrium dissociation constant (K{sub D}) for cyanide binding to this G. dibranchiata monomer methemoglobin has a numerical upper limit that is at least 2 orders of magnitude smaller than the value reported before the kinetic results were known.

• OSTI ID: 7189724
• Journal Information: Biochemistry; (USA), Vol. 27:21; ISSN 0006-2960
• Country of Publication: United States
• Language: English

Related Subjects

63 RADIATION, THERMAL, AND OTHER ENVIRON. POLLUTANT EFFECTS ON LIVING ORGS. AND BIOL. MAT.
59 BASIC BIOLOGICAL SCIENCES
CYANIDES
BIOLOGICAL EFFECTS
METHEMOGLOBIN
BIOCHEMICAL REACTION KINETICS
INVERTEBRATES
PH VALUE
ULTRAVIOLET SPECTRA
VISIBLE SPECTRA
ANIMALS
CARBOXYLIC ACIDS
GLOBINS
HEMOGLOBIN
HETEROCYCLIC ACIDS
HETEROCYCLIC COMPOUNDS
KINETICS
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
PIGMENTS
PORPHYRINS
PROTEINS
REACTION KINETICS
SPECTRA
560300* - Chemicals Metabolism & Toxicology
550200 - Biochemistry