Kinetics of photoinhibition in hydroxylamine-extracted photosystem II membranes: relevance to photoactivation and sites of electron donation

• Published in: Biochemistry (Easton) 1990-05, Vol.29 (21), p.5109-5118
• Main Authors: Blubaugh, Danny J, Cheniae, George M
• Format: Article
• Language: English
• Subjects: 550200 - Biochemistry; AMINO ACIDS; BASIC BIOLOGICAL SCIENCES; Binding, Competitive; BIOCHEMICAL REACTION KINETICS; Biological and medical sciences; CARBOXYLIC ACIDS; Cell Membrane - metabolism; Cell structures and functions; CHEMICAL REACTIONS; CHLOROPHYLL; Chlorophyll - metabolism; Chlorophyll A; Chloroplast, photosynthetic membrane and photosynthesis; Diphenylcarbazide - metabolism; ELECTROMAGNETIC RADIATION; ELECTRON TRANSFER; ELECTRONS; ELEMENTARY PARTICLES; FERMIONS; FLUORESCENCE; Fundamental and applied biological sciences. Psychology; HETEROCYCLIC ACIDS; HETEROCYCLIC COMPOUNDS; HYDROXY ACIDS; Hydroxylamines; KINETICS; LEPTONS; Light-Harvesting Protein Complexes; LUMINESCENCE; Manganese - metabolism; MEMBRANES; Molecular and cellular biology; ORGANIC ACIDS; ORGANIC COMPOUNDS; ORGANIC NITROGEN COMPOUNDS; Oxidation-Reduction; photoinhibition; PHOTOSYNTHETIC MEMBRANES; Photosynthetic Reaction Center Complex Proteins; PHOTOSYNTHETIC REACTION CENTERS; photosystem II; Photosystem II Protein Complex; PHYTOCHROMES; PIGMENTS; Plant Proteins - metabolism; Plants - metabolism; PORPHYRINS; PROTEINS; Quantum Theory; RADIATIONS; REACTION KINETICS; REDOX REACTIONS; TYROSINE; Tyrosine - metabolism; VISIBLE RADIATION
• ISSN: 0006-2960; 1520-4995
• DOI: 10.1021/bi00473a016

Kinetic analyses were made of the effects of weak-light photoinhibition on the capacity of NH2OH-extracted photosystem II membranes to photooxidize the exogenous electron donors Mn2+, diphenylcarbazide, and I- or to assemble functional water-oxidizing complexes during photoactivation. The loss of capacity for photooxidation of the donors showed two first-order components (half-times of 2-3 min and 1-4 h) with relative amplitudes dependent on the donor, suggesting two photodamageable sites of electron donation (sites 1 and 2, respectively), a conclusion confirmed by analyses of velocity curves of electron donation by each donor. All of the donors appear to be oxidized preferentially by site 1 both at saturating and at limiting light intensity; however, the contribution by site 2 was nearly comparable in saturating light. Loss of photoactivation also exhibited biphasic kinetics, with components having half-times of approximately 0.8 and 3.2 min. The major component (t1/2 = 3.2 min) corresponded to loss of site 1; essentially no photoactivation was observed after its loss. From these and other analyses, we conclude (1) the relative contributions of site 1 and site 2 to the photooxidation of various exogenous electron donors is determined largely by the rates of equilibration of the donors with the two sites, and (2) only site 1 contributes to photoactivation of the water-oxidizing complex. Site 1 is attributed to tyrosine Z of the reaction center's D1 polypeptide. The molecular identity of site 2 is unknown but may be tyrosine D of the D2 polypeptide.