REPAIR OF PHOTOINHIBITORY DAMAGE IN ANACYSTIS NIDULANS 625 (SYNECHOCOCCUS 6301): RELATION TO CATALYTIC CAPACITY FOR, AND ENERGY SUPPLY TO, PROTEIN SYNTHESIS, AND IMPLICATIONS FOR μmax AND THE EFFICIENCY OF LIGHT‐LIMITED GROWTH

Abstract

SummaryPreviously published data on photoinhibition in Anacystis nidulans (Richt.) Drouet 625 (=Synechococcus Naeg. 6301) in the presence (gross rate) and absence (net rate) of an inhibitor of protein synthesis, and on the rate of repair of photoinhibitory damage, are analysed. The analysis makes assumptions about the relationship between changes in the efficiency of photosynthesis and changes in the number of undamaged photoreaction two reaction centres, the number of photoreaction centres of photoreaction two per unit cell volume, and the Mr of the photodamageable polypeptide associated with photoreaction two. With this background, the rate of protein synthesis (mol amino acid incorporated (m3 cell volume)−1 s−1) which is required to just balance the rate of protein destruction in gross photoinhibition, or to support the rate of protein synthesis in repair, is computed. The conclusions drawn from this analysis are:(1) Repair of (gross) photodamage which is known to be submaximal requires rates of protein synthesis up to 1/10 of the rate of net protein synthesis at the μmax of Anacystis nidulans, and about 1/50 of the maximum possible capacity for protein synthesis deduced from the RNA content of Anacystis nidulans and the RNA‐based protein synthesis capacity of Escherichia coli.(2) The rates of protein synthesis computed in (1) use up to 1/5 of the ATP production rate from oxidative phosphorylation in darkness and up to 1/10 of the ATP production rate (including photophosphorylation) at an incident photon flux density of 5 μmol photon (400 to 700nm)m−2 s−1(3) Cells subject to photoinhibitory damage, and its repair, have an additional requirement for protein synthesis and ATP generation over cells not subject to photoinhibition. These additional requirements may limit both μmax and the efficiency of light‐limited growth.