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Interactions of Ca/sup 2 +/ and H/sup +/ with heme A in cytochrome oxidase

Journal Article · · J. Bioenerg. Biomembr.; (United States)
DOI:https://doi.org/10.1007/BF00744692· OSTI ID:5615284
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Ca/sup 2 +/ ions shift the absorption spectrum of reduced cytochrome a in mitochondria by acting from the outside of the membrane. In isolated cytochrome oxidase the shift may be induced by either Ca/sup 2 +/ or H/sup +/, the apparent pK varying between 6.20 and 5.75 depending on the state of cytochrome a3. Studies of the Soret band show that Ca/sup 2 +/ also shifts the spectrum of ferrocytochrome a3 in isolated oxidase in contrast to the situation in mitochondria or isolated oxidase reconstituted into liposomes. Model studies with reduced bis-imidazole heme A reveals an analogous spectral shift induced by Ca/sup 2 +/. Esterification of the propionate carboxyls of heme A abolishes the spectral shift, suggesting that it is due to interaction of Ca/sup 2 +/ with these groups. When taken together with the data with intact mitochondria, this suggests that the propionate side chains of cytochrome a are accessible to Ca/sup 2 +/ and H/sup +/ from the outside of the mitochondrial membrane. In the soluble enzyme both hemes a and a3 are accessible. Thus heme a may be located near the outside of the inner membrane whereas heme a3 experiences a different environment in which no Ca/sup 2 +/ shift occurs.

OSTI ID:
5615284
Journal Information:
J. Bioenerg. Biomembr.; (United States), Journal Name: J. Bioenerg. Biomembr.; (United States) Vol. 12:3-4; ISSN JBBID
Country of Publication:
United States
Language:
English

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Related Subjects

550200* -- Biochemistry
550300 -- Cytology
59 BASIC BIOLOGICAL SCIENCES
ABSORPTION SPECTRA
BIOCHEMICAL REACTION KINETICS
BIOLOGICAL EFFECTS
CALCIUM IONS
CARBOXYLIC ACIDS
CELL CONSTITUENTS
CELL MEMBRANES
CHARGED PARTICLES
CYTOCHROME OXIDASE
CYTOCHROMES
ENZYME ACTIVITY
ENZYMES
HAEM DEHYDROGENASES
HEME
HETEROCYCLIC ACIDS
HETEROCYCLIC COMPOUNDS
HYDROGEN IONS
IONS
KINETICS
MEMBRANES
MITOCHONDRIA
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
ORGANOIDS
OXIDOREDUCTASES
PIGMENTS
PORPHYRINS
REACTION KINETICS
SPECTRA