Biomaterial Database

Anomalously slow cyanide binding to Glycera dibranchiata monomer methemoglobin component II: implication for the equilibrium constant. 1988

J Mintorovitch, and J D Satterlee

Department of Chemistry, University of New Mexico, Albuquerque 87131.

In comparison to sperm whale metmyoglobin, metleghemoglobin a, 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. At 20 degrees C, with micromolar protein concentrations, kobsd varies between 9.11 x 10(-5) s-1 at pH 6.0, 100-fold KCN mole excess, and 1.12 x 10(-2) s-1 at pH 9.0, 250-fold KCN mole excess. Our analysis shows that the concentration-independent bimolecular rate constant (k1app) is small in comparison to those of the other heme proteins. For example, at pH 7.0 it is 0.491 M-1 s-1, compared to 1.1 x 10(5) M-1 s-1 for cytochrome c peroxidase; 111 M-1 s-1 for guinea pig methemoglobin; approximately 400 M-1 s-1 for sperm whale metmyoglobin; and 692 M-1 s-1 for soybean metleghemoglobin a, at the same pH and similar temperatures. Furthermore, our results show that the dissociation rate is extremely slow, with k-1app no larger than 10(-6) s-1. Separation of the bimolecular rate constant into contributions from kCN- (the rate constant for CN- binding) and from kHCN (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.(ABSTRACT TRUNCATED AT 250 WORDS)

UI	MeSH Term	Description	Entries
D007700	Kinetics	The rate dynamics in chemical or physical systems.
D008706	Methemoglobin		Ferrihemoglobin
D011077	Polychaeta	A class of marine annelids including sandworms, tube worms, clamworms, and fire worms. It includes also the genus Myxicola infundibulum.	Myxicola,Myxicolas,Polychaetas
D011190	Potassium Cyanide	A highly poisonous compound that is an inhibitor of many metabolic processes, but has been shown to be an especially potent inhibitor of heme enzymes and hemeproteins. It is used in many industrial processes.	Potassium Cyanide (K(14)CN),Potassium Cyanide (K(C(15)N)),Cyanide, Potassium
D011485	Protein Binding	The process in which substances, either endogenous or exogenous, bind to proteins, peptides, enzymes, protein precursors, or allied compounds. Specific protein-binding measures are often used as assays in diagnostic assessments.	Plasma Protein Binding Capacity,Binding, Protein
D003486	Cyanides	Inorganic salts of HYDROGEN CYANIDE containing the -CN radical. The concept also includes isocyanides. It is distinguished from NITRILES, which denotes organic compounds containing the -CN radical.	Cyanide,Isocyanide,Isocyanides
D006863	Hydrogen-Ion Concentration	The normality of a solution with respect to HYDROGEN ions; H+. It is related to acidity measurements in most cases by pH	pH,Concentration, Hydrogen-Ion,Concentrations, Hydrogen-Ion,Hydrogen Ion Concentration,Hydrogen-Ion Concentrations
D000818	Animals	Unicellular or multicellular, heterotrophic organisms, that have sensation and the power of voluntary movement. Under the older five kingdom paradigm, Animalia was one of the kingdoms. Under the modern three domain model, Animalia represents one of the many groups in the domain EUKARYOTA.	Animal,Metazoa,Animalia
D013053	Spectrophotometry	The art or process of comparing photometrically the relative intensities of the light in different parts of the spectrum.