A non-fluorescent complex of chlorophyll a with plastocyanin.

A complex between chlorophyll a and plastocyanin has been prepared by dialysis of mixtures of chlorophyll in Triton X-100 micellar solution with the protein. The complex appears to contain no more than one chlorophyll per plastocyanin molecule, and is non-fluorescent, whether the protein is in the oxidized or reduced state. The lack of fluorescence suggests that the chlorophyll is adsorbed very close to the Cu center.

The effects of instructional set on the outcome of a stress management program.

A multicomponent stress management program, consisting of education about stress, various sorts of relaxation training, and cognitive coping strategies, was administered under two different instructional sets: In the positive demand set the program was touted to have previously been shown to be very effective, while in the neutral demand set the program was described as experimental. The two conditions were compared to a waiting list control. Results showed higher expectations of benefit in the positive demand group. Moreover, this group rated themselves as more able to cope with stress than the other two groups. Finally, the positive demand group showed significantly greater reductions in systolic blood pressure reactivity to laboratory stress tests (mental arithmetic and cold pressor) than the other two groups. The posttest advantages seemed to be mediated by a significantly higher level of home practice in the positive demand group.

Interaction between the intermediary electron acceptor (pheophytin) and a possible plastoquinone-iron complex in photosystem II reaction centers.

Photoreduction of the intermediary electron acceptor, pheophytin (Pheo), in photosystem II reaction centers of spinach chloroplasts or subchloroplast particles (TSF-II and TSF-IIa) at 220 K and redox potential E(h) = -450 mV produces an EPR doublet centered at g = 2.00 with a splitting of 52 G at 7 K in addition to a narrow signal attributed to Pheo([unk]) (g = 2.0033, DeltaH approximately 13 G). The doublet is eliminated after extraction of lyophilized TSF-II with hexane containing 0.13-0.16% methanol but is restored by reconstitution with plastoquinone A (alone or with beta-carotene) although not with vitamin K(1). TSF-II and TSF-IIa are found to contain approximately 2 nonheme Fe atoms per reaction center. Incubation with 0.55 M LiClO(4) plus 2.5 mM o-phenanthroline (but not with 0.55 M LiClO(4) alone) decreases this value to approximately 0.6 and completely eliminates the EPR doublet, but photoreduction of Pheo is not significantly affected. Partial restoration of the doublet (about 25%) was achieved by subsequent incubation with 0.2 mM Fe(2+), but not with either Mn(2+) or Mg(2+). The Fe removal results in the development of a photoinduced EPR signal (g = 2.0044 +/- 0.0003, DeltaH = 9.2 +/- 0.5 G) at E(h) = 50 mV, which is not observed after extraction with 0.16% methanol in hexane. It is ascribed to plastosemiquinone no longer coupled to Fe in photosystem II reaction centers. The results show that a complex of plastoquinone and Fe can act as the stable "primary" electron acceptor in photosystem II reaction centers and that the interaction of its singly reduced form with the reduced intermediary acceptor, Pheo([unk]), is responsible for the EPR doublet.

Further purification of "Triton subchloroplast fraction I" (TSF-I particles). Isolation of a cytochrome-free high-P-700 particle and a complex containing cytochromes f and b6, plastocyanin and iron-sulfur protein(s).

The "Triton Subchloroplast Fraction I" or "TSF-I particles" can be further fractionated into a cytochrome fraction and a P-700-containing fraction essentially free of cytochromes. The cytochrome complex contains cytochromes f and b6 in approx. equimolar amounts, and, in addition, also plastocyanin and one iron-sulfur protein, all in the bound state. Bound plastocyanin was characterized by EPR spectroscopy. The EPR spectrum of the bound iron-sulfur protein resembles that previously detected in Phostosystem I particles under highly reducing conditions at lower than -560 mV. The redox potential of P-700 in the cytochrome-free high-P-700 particles was measured to be +468 mV; those of cytochromes f and b6 are +345 and -140 mV, respectively. Among the four components present in the complex, only cytochrome f can be coupled to a Photosystem I particle and undergoes photooxidation. This coupled photooxidation is totoally inhibited by KCN and only partially inhibited by HgCl2. The similarity of the complex containing cytochromes f and b6, plastocyanin, and an iron-sulfur protein to complexes III and IV of the mitochondrial respiratory redox chain and a possible involvement of the complex in cyclic photophosphorylation are noted and discussed.

Photoreduction of 2,6-dichlorophenolindophenol by diphenylcarbazide: a photosystem 2 reaction catalyzed by tris-washed chloroplasts and subchloroplast fragments.

The use of diphenylcarbazide as an electron donor coupled to the photoreduction of 2,6-dichlorophenolindophenol by tris-washed chloroplasts or subchloroplast fragments provides a simple and sensitive assay for photosystem 2 of chloroplasts. By varying the concentration of tris buffer at pH 8.0 during an incubation period it is shown that the destruction of oxygen evolution activity is accompanied by a corresponding emergence of an ability to photooxidize diphenylcarbazide, as evidenced by absorbance changes due to diphenylcarbazide at 300 nm. The temperature-sensitive oxidation of diphenylcarbazide is inhibited by DCMU and by high ionic strengths. This activity appears to measure the primary photochemical reaction of photosystem 2.