Biomedical subjects

B Chance

Publications and source records attributed to B Chance.

At least 613 records · Page 34Linked to original sources

PubMed1970

Energy-coupling mechanisms in mitochondria: kinetic, spectroscopic, and thermodynamic properties of an energy-transducing form of cytochrome b.

The primary event of coupled electron transfer at phosphorylation site II is identified with a modification in one of the two chemically distinct forms of cytochrome b, designated as the energy-transducing cytochrome b(T). This modification is expressed through a change in the redox midpoint potential and by an increase in its reaction half time with cytochrome c(1). In pigeon heart mitochondria cytochrome b(T) exhibits an absorption maximum at 564 nm and on this basis, it can be distinguished from Keilin's cytochrome b which exhibits an absorption maximum at 560 nm and serves as an electron carrier on the substrate side of cytochrome b(T). Kinetic capability of cytochrome b(T) is evidenced by its rapid electron transfer and energization time of less than 200 msec, its thermodynamic capability-by a 280 mV potential span suitable for providing one of the two electron transfer reactions required in ATP formation. Two secondary events of coupled electron flow may be identified with a charge separation across the lipid structure of the permeability barrier and a change in water structure; both events result in an increased 1-anilino-8-naphthalene-sulfonic acid (ANS) response to the altered environment.

Animals↗

PubMed1970

Fluorescent probe environment and the structural and charge changes in energy coupling of mitochondrial membranes.

The use of fluorescent probes to give continuous readouts of the structural states of mitochondrial membranes during energy coupling seems a logical extension of their use in the study of protein structural changes. A clear correlation of the probes' fluorescence characteristics with the acquisition of energy coupling can be demonstrated in fragmented and natural membrane using 1-anilinonaphthalene-8-sulfonate (ANS) and ethidium bromide respectively. The present contribution attempts to bring together contemporary viewpoints of this and other laboratories and the recent experimental data and give some detailed information on probe environment and on the structural or charge changes occurring upon energization. The energy-dependent region of the membrane is located at an aqueous interface between an outer layer of proteins (presumably cytochromes) and the membrane permeability barrier; the aromatic portion of ANS appears to be located in the lipid phase and the sulfonic acid group in the aqueous phase. The aqueous phase is probably a structured water region near paramagnetic membrane components such as cytochrome. Membrane energization arising from altered redox potential changes of cytochromes (b(T)) is communicated to the water structure through altered structural states of the hemoproteins, causing a decreased volume of the structured water region and increased interaction with the paramagnetic components in the energized state. Attendant alterations of protonic equilibria of membrane components induce both local and transmembrane changes in charge distribution, with consequent movements of ions, including the probe molecules themselves.

Animals↗

PubMed1970

Energy and Electron Transfer Systems of Chlamydomonas reinhardi: II. Two Cyclic Pathways of Photosynthetic Electron Transfer in the Pale Green Mutant.

Light- and oxygen-induced changes of cytochromes f, b(563), and b(559) and ferredoxin-flavoprotein were studied by a double beam spectrophotometer with combinations of inhibitors and lowered temperatures in the whole cells of the pale green mutant of Chlamydomonas reinhardi (ATCC 18302). At room temperature, the steady state changes of cytochrome f and ferredoxin-flavoprotein are small, but at low temperature slightly above 0 C, they are clearly defined. Phenylmercuric acetate inhibits photoreduction of ferredoxin-flavoprotein and cytochrome f simultaneously but not that of cytochrome b(563). 2-Heptyl-4-hydroxyquinoline-N-oxide shows a crossover point between cytochromes f and b(563) and partially inhibits photoreduction of cytochrome f. Two cyclic pathways operating in C. remhardi are postulated: (a) photosystem I --> x --> b(563) --> f --> photosystem I; and (b) photosystem I --> x --> ferredoxin-flavoprotein --> f --> photosystem I.

Journal Article↗

PubMed1970