Further purification of "Triton subchloroplast fraction I" (TSF-I particles). Isolation of a cytochrome-free high-P-700 particle and a complex containing cytochromes f and b6, plastocyanin and iron-sulfur protein(s)

The "Triton Subchloroplast Fraction I" or "TSF-I particles" can be further fractionated into a cytochrome fraction and a P-700-containing fraction essentially free of cytochromes. The cytochrome complex contains cytochromes f and b6 in approx. equimolar amounts, and, in addition, also plastocyanin and one iron-sulfur protein, all in the bound state. Bound plastocyanin was characterized by EPR spectroscopy. The EPR spectrum of the bound iron-sulfur protein resembles that previously detected in Phostosystem I particles under highly reducing conditions at lower than -560 mV. The redox potential of P-700 in the cytochrome-free high-P-700 particles was measured to be +468 mV; those of cytochromes f and b6 are +345 and -140 mV, respectively. Among the four components present in the complex, only cytochrome f can be coupled to a Photosystem I particle and undergoes photooxidation. This coupled photooxidation is totoally inhibited by KCN and only partially inhibited by HgCl2. The similarity of the complex containing cytochromes f and b6, plastocyanin, and an iron-sulfur protein to complexes III and IV of the mitochondrial respiratory redox chain and a possible involvement of the complex in cyclic photophosphorylation are noted and discussed.

A new photosynthetic pigment, "P430": its possible role as the priary electron acceptor of photosystem I

The technique of flash kinetic spectrophotometry was used to demonstrate a broad absorption band around 430 nm, which was kinetically different from P700, in several photosystem-I particles from spinach and blue-green algae. The component represented by this absorption band, designated as "P430", was bleached as fast as P700. Its recovery in the dark was accelerated by ferredoxin and by various artificial electron acceptors with redox potentials as low as -521 mV. The recovery kinetics have been demonstrated to be identical to those of a concomitant reduction of several of the artificial electron acceptors used. Tentatively, "P430" has been proposed as a possible primary electron acceptor of photosystem I.

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.

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.