Firefly luminescence in the study of energy transfer mechanisms. II. Adenosine triphosphate and photosynthesis

Abstract

1. 1. The influence of light and other environmental factors on the adenosine triphosphate (ATP) content of Chlorella pyrenoidosa has been investigated, using the firefly luminescent system as an assay tool. Light has been found to cause large and rapid changes in the ATP levels of these algae. 2. 2. After a period of dark anaerobiosis, the ATP level rises on illumination or admission of air to higher levels (2–10 times dark levels). ATP levels with respect to time in light show a maximum at ca. 1 min.; thereafter, a decrease. The minimum calculated yield of P:O 2 is 1:6, but the actual values for rate of formation are probably considerably higher. 3. 3. The production of ATP by oxygen is inhibited to a greater extent by low temperatures than is light-induced ATP formation. 4. 4. The rate of ATP formation saturates at high light intensities, whereas the steady-state concentrations of ATP exhibit a maximum at low light intensities. 5. 5. Illumination causes a decrease in the ATP after a period of dark aerobiosis, and the subsequent dark period is characterized by a rapid increase in the ATP level. This effect is observable in the presence or absence of CO 2, indicating that the ATP-utilizing reactions are largely prior to or independent of carboxylation reactions. 6. 6. The time constants of these transient ATP changes are of the order of magnitude of other photosynthesis induction periods (1–3 min.) and relatively independent of intensity. 7. 7. It is suggested that these results are consistent with and lend support to the theory that ATP is both generated and utilized by lightdriven reactions, and that one major drain on the ATP content is the production of reducing material capable of reversible reaction with a system at the oxidation-reduction potential of carbohydrate. The relation of previous observations to these results and to the chemophotosynthetic mechanism of photosynthesis postulated is pointed out.