A Comparison of Decay Kinetics of Photo‐produced Absorbance, Epr, and Luminescence Changes in Chromatophores of Rhodospirrillum Rubrum*

Abstract

–Quantitative comparison of the decay rate for absorbance photochanges in chromatophores of R. rubrum at the major wavelengths of peaks and troughs (280, 365, 385, 433, 605, 763, 790, 810, 850, 865, 890 nm) reveal no major differences under a variety of sample conditions. In addition, the decay kinetics of EPR phtochange at the two environmental potentials used in this study are identical with the absorbance ph;otochange decay. Decay curves for fresh chromatophores, aged chromatophores, and fresh chromatophores at high ionic strength display a variety of half times and curve shapes. All of these data however, may be fit (within 10 per cent) by the equation x=αe8.2t+βe0.18t by merely varying the values of α and β. This is interpreted as meaning that any single trapping site may exist in one of two major forms each of which decays following a first order or pseudo‐first order reaction. Although the change in decay pattern upon aging is not reversible, that due to high ionic strength is. The time dependencies for two light emission phenomena have been measured as well as their response to the oxidation state of molecules at the trapping site. A major component of long‐lived luminescence follows pseudo‐second order kinetics with a half time of 38 msec. A very long lived luminescence shows an increse with time which is nearly proportional to the decay of absorbance photochanges.

Electron Spin Resonance of Chlorophyll and the Origin of Signal I in Photosynthesis

“…The most prominent of the photo-esr signals (Signal I) is rapidly reversible, has the free electron gvalue 2.0025, a peak-to-peak linewidth (AH) of about 7.5 g (plants) or about 9.5 g (bacteria), a Gaussian line shape, and no hyperfine structure. Subsequent esr studies (critically reviewed by Weaver (2)) on chloroplast or chromatophore preparations (3)(4)(5)(6), active-center preparations (7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19), organisms of unusual isotopic composition (20,21), and on in vitro chlorophyll systems (21)(22)(23)(24)(25)(26)(27)(28)(29)(30)(31) have made it probable that Signal I arises by the photooxidation of special chlorophyll molecules located in the photosynthetic reaction center, and that this is the chlorophyll responsible for the long-wavelength absorption associated with the reaction center (32) (P700, plants; or P870, bacteria). It has further been suggested (21) that Signal I is due to the formation of Chl+-or BChl+-; however, Signal I is much narrower than the esr signals recorded from Chl+.. To explain the unusual esr and spectral properties of reaction-center chlorophyll, chlorophyll aggregation of an unspecified nature (33), chlorophyll-lipid and chlorophyll-protein interactions (34), or perturbations in the chlorophyll -r system caused by unspecified changes in the environment (24) have been suggested.…”

A Survey of Epr Investigations of Bacterial Photosynthesis

“…In fact, Loach and Hall (1972), using iron-deficient sub-chromatophores prepared from R. rubrum, observed a photo-produced free-radical signal with a y-value of 2.005 f 0.0003 and a peak-to-peak linewidth of 7 f 0.3 G the signal shown in Fig. 3, the solid line.…”

“…These studies were conducted at room temperature with chromatophores of R. rubrum (Loach and Sekura, 1967) and reaction centers of R. spheroides (Bolton et ul., 1969;Warden and Bolton, 1976); and, at cryogenic temperatures (McElroy et ul., 1969;McElroy et al, 1974) with whole cells and chromatophores of R. rubrum and its G-9 mutant, R. spheroides and Chromatiunz and also reaction centers of R. spheroides. Only Warden and Bolton (1 976) measured the decay kinetics simultaneously.…”

“…In addition, those systems in which iron has been removed still exhibit the photoproduction of the P870t cation radical and the optical density changes associated with the oxidation of P870 (Loach and Hall, 1972;Feher et al, 1972). McElroy et al (1974) found that the decay of the changes associated with P870 in R. spheroides reaction centers to be temperature independent between 1.5 and 80 K. They proposed that the decay occurs via an electron tunneling through a potential barrier.…”

Biological Magnetic Resonance

“…Furthermore, signal B1 is photoproduced at cryogenic temperatures, an observation which is requisite for assignment of this resonance to the primary photochemical act (And roes et aI., 1962;Cost et aI., 1969;McElroy et al, 1969). The kinetic equivalence of P870 oxidation and reduction with signal B1 formation and decay has been established at room temperature in chromatophores (Loach and Sekura, 1967), and reaction centers and at 4°K in reaction centers and chromatophores (McElroy et aI., 1969(McElroy et aI., , 1974. Furthermore, quantitative ESR and optical measurements demonstrate conclusively that P870 and signal B1 are present in stoichiometric equivalence (Loach and Walsh, 1969;Bolton et al, 1969;.…”