Incubation of class II chloroplasts of spinach with copper in the light at pH = 8 in concentrations that inhibit oxygen evolution results in the formation of a copper (II) protein complex with the photosynthetic membrane. The EPR spectra indicate that the four nearest ligands to Cu(II) consist of three oxygen atoms and one nitrogen atom. The copper (II) protein appears to be pre dominantly associated with photosystem II. The formation of this protein as measured by the EPR signal amplitude of its room temperature spectrum correlates with the inhibition of oxygen evolution and of electron transport within photosystem I. This result indicates that the inhibition of photosynthetic electron transport by copper may be due to the formation of a copper (II) chelate with a membrane protein.
E.s.r. investigations of the reaction products of Cu(OH)* suspended in methanol with H 2 0 2 reveal that depending on the mole ratio of H202 to Cu(OI-I), several as yet unknown polycrystalline copper(I1)-peroxide intermediate compounds, predominantly with non-cubic microsymmetry, are formed. On addition of excess of H202 no e.s.r. signal was obtained in the range 0-11 000 G in neutral and alkaline suspensions indicating the formation of copper(1) compounds. At 90 K a single line at g = 0.85 with a half width of approximately 4000 G was obtained for polycrystalline Cu(OH), samples. At room temperature no signal was observed. A rough estimate of the spin lattice relaxation time leads to a value of about s at 90 K indicating the existence of a near-by excited state. The e.s.r. spectra of copper peroxide powders at 90K were identical with that of polycrystalline CU(OH)~. This was interpreted on the assumption that the crystal structure of copper peroxide prepared under the usual conditions is quite similar to that of copper hydroxide which argues in favour of its interpretation as a copper hydroperoxide compound. No e.s.r. signals due to CuO or HOz radicals were found in copper peroxide powders or in neutral suspensions. This rules out the structure hypothesis suggested by Glasner and by Teletov and Veleshinetz.
Intoxication of class II chloroplasts of spinach with Cu(II) leads to inhibition of millisecond luminescence. The degree of inhibition depends on Cu (II) -concentration. The investgation of the pH dpendence of the inhibition curve of luminescence revealed that (1) there is an inhibition site of copper on the donor side of photosystem II, (2) copper (II) does not act as an uncoupler of photophosphorylation, (3) a protonation equilibrium is involved in the inhibition mechanism, and (4) copper (II) binds to a dissociated residue of a membrane protein.
Abstract— An alternative method to that used by Mar and Roy (1974) for the determination of the kinetics of the back reaction of photosystem II from the luminescence decay curve in the presence of 3–(3,4‐dichlorophenyl)‐1,1‐dimethylurea (DCMU) has been suggested. The new theory relies upon two hypotheses: the well‐known recombination hypothesis of luminescence and the assumption that the luminescence yield in the seconds region is given by the variable part of the live fluorescence yield. The second hypothesis was introduced since assuming a constant luminescence yield results in kinetic data that are not consistent with measurements of the kinetics of the back reaction by the restoration of the area over the fluorescence rise curve. The dependence of the live fluorescence yield from the concentration of closed PS II traps was assumed to be represented by Delosme's expression originally derived for the rise curve of the fluorescence yield in the presence of DCMU.
The theory is based on the fact that then the partial and total light sums of luminescence are simple functions of the concentration of the primary electron acceptor Q‐ of PS II. Thus, after integrating the luminescence decay curve the theory permits a convenient evaluation of the kinetics of the back reaction [Q‐](t) in terms of the partial and total light sum.
This method was applied in order to determine the kinetics of the back reaction in Chlorella fusca in the presence of DCMU. It is shown that the kinetics of deactivation of the S, state can be described using the expression for the kinetics of the back reaction derived by Mar and Roy. As an alternative explanation, a biphasic first order decay of S2 is proposed.
W/~hrend 2,4 wahrseheinlich die obere Grenze fiir den Dq/B-Wer$ fluoreszierender Cr(3)-Komplexe ist, gibt es ffir die Existenz eines unteren Grenzwerts keine Anzeichen.Experimentefle Ergebnisse legen nahe, dab das Verh~iltnis yon Phosphoreszenz-zu Fluoreszenzemission dutch die relative H6he der Minima der ~Eg-und 4T~g-Potentialkurven bestimmt wird.Whereas 2.4 is likely to be an upper limit for the Dq/B-value of Cr(3)-eomplexes which show fluorescence the existence of a lower bound is rather unlikdy.Experimental evidence suggests that the energy difference between the minima of the ~Eg-and the 4T2g-potential curves is one of ~he factors determining the relative intensities of phosphorescence and fluorescence.Alors que 2,4 apparait eomme une limite sup6rieure du rappor~ Dq/B pour les complexes fluoreseents de Cr(3), l'existenee d'une limite inf6rieure est peu probable. L'6videnee exp6ri-mentale suggbre que l'intensit6 relative de la phosphorenee et de la fluorescence est d6ter-min6e par la diff6renee d'6nergie entre les minima des eourbes de potentiel des 6tats ~Eg et 4T2~.
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