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Biomedical subjects

B Ke

Publications and source records attributed to B Ke.

At least 73 records · Page 4Linked to original sources
PubMed1970

The relation of the 515 nanometers absorbance change to adenosine triphosphate formation in chloroplasts and digitonin subchloroplast particles.

The flash-induced absorbance changes at 515 nanometers has been studied in chloroplasts and in digitonin subchloroplast particles of lettuce. The effect of various conditions and uncouplers was tested on the decay kinetics of this absorbance change and on ATP formation in the presence of phenazine methosulphate, either by continuous or flash illumination. It has been found that in chloroplasts, carbonyl cyanide m-chloromethoxyphenylhydrazone and nigericin in the presence of K(+) accelerate the decay of the 515 change and inhibit ATP formation. However, under a variety of conditions the rate of decay of the 515 absorbance change was found to be unrelated to ATP formation. Preillumination, addition of valinomycin in the presence of K(+), addition of Na(+), or divalent cations accelerate the decay of the 515 absorbance change markedly but have no effect on ATP formation. Addition of phosphorylation reagents has no effect on the decay rate beyond that obtained by Mg(2+) and inorganic phosphate. NH(4)Cl, and to some extent atebrin, while inhibiting ATP formation, do not affect the decay of the 515 absorbance change.In digitonin subchloroplast particles the decay kinetics of the absorbance change resemble that of chloroplasts, but the magnitude of the change is smaller. The pH change in this preparation is reduced much more than the 515 absorbance change.According to the chemiosmotic hypothesis, the sum of DeltaE(membrane potential) and DeltapH is the driving force for ATP formation. The lack of an increase in DeltaE in digitonin subchloroplast particles, which are practically devoid of DeltapH and have a normal ATP-forming activity, is inconsistent with the chemiosmotic hypothesis.

Journal Article↗
PubMed1970

Photochemical characteristics in a soybean mutant.

Chloroplasts were isolated from wild type (DG) and heterozygous mutant (LG) soybean (Glycine max) leaves, and various biochemical functions were compared. Noncyclic electron transport, and its coupled phosphorylation, cyclic phosphorylation and H(+) ion transport in both systems, were 3 to 5 times faster in rate (on a chlorophyll basis) in the mutant plastids. On a chloroplast lamellar protein basis, the mutant plastid rates were 1.5 to 2.5 times the wild type rates.Plastoquinone (PQ) reduction and oxidation (rates and extent) were measured by following absorbance changes at 260 nanometers with the repetitive flash technique. Mutant plastids have about a 2-fold greater apparent first order rate constant for PQ oxidation and a 3- to 5-fold larger pool of rapidly reducible PQ. Plastoquinone oxidation has been identified by other workers as the rate-limiting step in electron transport. Assuming the PQ oxidation is a first order process (d(PQH(2))/dt = k(D)[PQH(2)]t), the observed increase in k(d) for the LG (k(d) (LG) approximately 2k(d) (DG)) and the greater steady state amount of rapidly turning over PQ, [PQH(2)](LG)>[PQH(2)](DG), could account for the 3- to 5-fold greater rates of electron transport and phosphorylation found in the mutant chloroplasts.Light saturation for noncyclic photophosphorylation and photosystem 2 plus 1 electron transport occurred at similar intensities for both LG and DG plastids. Relative quantum requirements extrapolated to zero intensity were similar in the LG and DG, although at finite light intensities the LG had a better relative quantum efficiency.Ammonium chloride concentrations needed to inhibit cyclic photophosphorylation 50% were similar in both LG and DG plastids. Nigericin, poly-l-lysine, and chlorotri-n-butyltin, were needed in concentrations 5 to 10 times greater in the LG to yield 50% inhibition at comparable chlorophyll concentrations.

Journal Article↗