Effects of chemical modifications of heme on kinetics of carbon monoxide binding to free home
The rates of carbon monoxide recombination to six different kinds of chemically modified heme with various substituents at positions 2 and 4 have been studied in the protein-free state (free heme) by the laser flash photolysis method in a mixture of ethylene glycol and 0.02 N NaOH (80:20, v/v) (80% ethylene glycol). The carbon monoxide combination rate constants to the various free hemes obtained in 80% ethylene glycol at 22/sup 0/ were 1.4, 2.1, 2.1, 3.7, 4.5, and 6.4 x 10/sup 7/ M/sup -1/ s/sup -1/ for 2,4-diformyl-, spirographis (2-formyl-4-vinyl-), isospirographis (2-vinyl-4-formyl-) proto-(2,4-divinyl-), deutero-(2,4-dihydrogen-), and meso-(2,4-diethyl-), hemes, respectively. This order of increase in carbon monoxide combination rate constants for these hemes correlates exactly with decrease in electron attractivity of heme side chains (i.e., increase in pK/sub 3/, basicity of nitrogen base of prophyrin) and is completely opposite to that obtained for carbon monoxide binding to these hemes reconstituted with apomyoglobin. Contrary to the results for myoglobin, the two isomers of monoformyl-monovinylheme exhibited similar optical properties and the same combination rate constant indicating that the differences in the optical and kinetic results observed in myoglobin are due to different interactions of these isomeric hemes with protein.
- Research Organization:
- Children's Hospital of Philadelphia, PA
- OSTI ID:
- 5143515
- Journal Information:
- J. Biol. Chem.; (United States), Journal Name: J. Biol. Chem.; (United States) Vol. 252:21; ISSN JBCHA
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
59 BASIC BIOLOGICAL SCIENCES
BINDING ENERGY
CARBON COMPOUNDS
CARBON MONOXIDE
CARBON OXIDES
CARBOXYLIC ACIDS
CHALCOGENIDES
CHEMICAL REACTION KINETICS
CHEMICAL REACTIONS
DECOMPOSITION
ENERGY
HEME
HETEROCYCLIC ACIDS
HETEROCYCLIC COMPOUNDS
KINETICS
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
OXIDES
OXYGEN COMPOUNDS
PHOTOCHEMICAL REACTIONS
PHOTOLYSIS
PIGMENTS
PORPHYRINS
REACTION KINETICS