Spectrophotometric Isolation of Kinetically Different Pools of P-700 and Their Correlation to the Reduction of NADP by Isolated Chloroplasts *. I. The Effect of Light Quality and Intensity
Zeitschrift für Naturforschung C - A Journal of Biosciences
Excitation of isolated chloroplasts in the presence of ferredoxin and NADP by repeated short flashes yields a polyphasic absorption change at 700 nm. Assuming first-order reactions, the signal may be resolved into three distinct components with average relaxation times of approximately 20 μs, 150 μs and 20 ms. Their relative magnitude is dependent on experimental conditions; their spectral characteristics indicate that all three components may be ascribed to P-700. Concurrent measurements of
... NADPH, the flash yield of NADP reduction with an enzymatic recycling method, allowed Y-NADPH to be compared to the magnitude of each of the three P-700 components and to total P-700. In general, the data show a good correlation of NADP reduction with the sum of the μs-phases but not with the ms-phase or total P-700. Analysis of light intensity curves (blue or far red flashes) with a mathematical model which yields maximum values for all parameters at infinite light intensity shows that in both cases approximately two moles of the microsecond component of P-700 turn over for each mole of NADPH formed. In contrast, the molar ratio of the ms-component to the yield of NADP reduction is approx. 0.2 in blue and approx. 6.3 in far red light. The data suggest that only that portion of the P-700 pool which relaxes in the microsecond range may be involved in the reduction of NADP while the ms-component is funtionally isolated from linear electron transport.