Kinetics of Nicotinamide Adenine Dinucleotides during Dark‐Light Transients in <i>Chlorella</i>

Abstract Nicotinamide adenine dinucleotides were extracted and assayed at frequent intervals for 30 seconds prior to and 60 seconds immediately following illumination of Chlorella cells. For these experiments a special illumination vessel was designed which dispensed 1 ml aliquots of algae with no dead volume. —White incandescent illumination of aerated Chlorella caused an immediate oxidation of its pyridine nucleotides. Under similar conditions blue light caused an initial reduction of these coenzymes. — White illumination of the alga perfused with CO 2 ‐free air caused a transitory reduction of the pyridine nucleotide followed by an oxidation and a second reduction, Blue light, under similar conditions caused an immediate reduction but no oxidation as seen with white light. — When suspensions were perfused with N 2 , illumination produced a prompt and rapid oxidation of NADH. The extent of this oxidation was greater in white than in blue light. Under these conditions NADP + was initially reduced and subsequently, temporarily oxidised. — The evidence offers some support for Lundegårdh's theory that blue light is more effective than red light in the photo‐reduction of NADP + . The results are discussed with referemce to the demonstrated in vitro reduction of nicotinamide adenine dinucleotides by chloroplasts and the conflicting reports from in vivo kinetic studies of living photosynthetic organisms. A scheme is proposed to explain the nicotinamide adenine dinucleotide kinetics as observed in these experiments.