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Abstract A recent proteomic analysis of the thylakoid lumen of Arabidopsis thaliana revealed the presence of several PsbP-like proteins, and a homologue to this gene family was detected in the genome of the cyanobacterium Synechocystis sp. PCC 6803 (Schubert M, Petersson UA, Haas BJ, Funk C, Schröder WP, Kieselbach T (2002) J Biol Chem 277, 8354–8365). Using a peptide-directed antibody against this cyanobacterial PsbP-like protein (sll1418) we could show that it was localized in the thylakoid membrane and associated with Photosystem II. While salt washes did not remove the PsbP-like protein from the thylakoid membrane, it was partially lost during the detergent-based isolation of PSII membrane fractions. In total cell extracts this protein is present in the same amount as the extrinsic PsbO protein. We did not see any significant functional difference between the wild-type and a PsbP-like insertion mutant.

When photosystem (PS) II-enriched membranes are exposed to strong light, cross-linking of the intrinsic D1 protein with the surrounding polypeptides and degradation of the D1 protein take place. The cross-linking of the D1 protein with the α-subunit of cytochrome b559is suggested to be an early event of photoinduced damage to the D1 protein (Barbato et al., FEBS Lett. 309 (1992) 165–169). The relationship between the cross-linking and the degradation of the D1 protein, however, is not yet clear. In the present study, we show that the addition of stromal extract from chloroplasts degrades the 41 kDa cross-linked product of D1/cytochrome b559α-subunit and enhances the degradation of the D1 protein. Incubation of the preilluminated PS II-enriched membranes with the stromal extract at 25°C causes the degradation of the cross-linked product by more than 70%. The activity of the stromal extract showed a pH optimum at 8.0, and was enhanced by the addition of ATP or GTP. Consistent with the nucleotide effect, this stromal activity was eliminated by the preincubation of the stromal extract with apyrase, which hydrolyzes nucleotides. Also, the stromal activity was nearly fully inhibited by a serine-type protease inhibitor, 3,4-dichloroisocoumarin, which suggests participation of a serine-type protease(s).

The secondary structure and thermal stability of the extrinsic 23 kDa protein (OEC23) of spinach photosystem II have been characterized in solution between 25 and 75°C using Fourier transform infrared spectroscopy. Quantitative analysis of the amide I band (1700–1600 cm−1) shows that OEC23 contains 5% α‐helix, 37% β‐sheet, 24% turn, and 34% disorder structures at 25°C. No appreciable conformational changes occur below 45°C. At elevated temperatures, the β‐sheet structure is unfolded into the disorder structure with a major conformational transition occurring at 55°C. Implications of these results for the functions of OEC23 in photosystem II are discussed.

Degradation of the reaction center-binding protein D1 of Photosystem II (PS II) during photoinhibition is dependent on the action of active oxygen species and/or D1-specific proteases. Protein conformational changes may be involved in the process of D1 degradation. In the present study, we determined the effect of H2O2on spinach PS II-enriched membranes and core complexes with respect to electron transport, Mn content and protein secondary structural changes as measured by Fourier transform infrared (FTIR) spectroscopy. H2O2is effective in removing catalytic Mn in PS II, especially in PS II core complexes depleted of OEC18 and OEC24, impairing the donor-side. By quantitative analysis of the amide I band (1600 – 1700 cm-1) with both aqueous and dehydrated PS II samples, we found that no significant secondary structural changes are associated with H2O2treatment in the dark, even though there is some cleavage of the D1 protein by H2O2treatment as determined by Western analysis with specific antibodies. In contrast, a large decrease in the α-helices in the PS II core occurs, with or without H2O2treatment, after 20 min strong illumination and there is more extensive degradation of the D1 protein. Our results suggest that high light enhances the cleavage of the D1 protein which is reflected in the large protein secondary structural changes in PS II detected by FTIR measurements.

The acoustic velocities and densities of 20 types of commercial rubber have been measured at a frequency of 2 MHz at room temperature, and they are evaluated in terms of their application to an acoustic lens or an acoustic window of probes of an ultrasonic diagnostic instrument. Fluorosilicone rubber and phoshazene rubber have lower acoustic velocities than the human body, and they have excellent impedance matching with the human body. Both the acoustic velocities and densities of butadiene rubber, polybutadiene rubber, acrylic rubber and polyurethane match those of the human body. It is also described that rubber having good impedance matching with the human body can be fabricated by adjusting the volume fraction of the added filler.

Modified lead titanate ceramics with exceptionally large electromechanical anisotropy (ratio of electromechanical coupling factor for thickness vibration to that for planar vibration is more than 15) are produced. These ceramics have a chemical formula (Pb1-(3x/2)Smx) (Ti1-yMny)O3. They are found to be very useful in ultrasonic probe applications due to their extremely small coupling factor of unwanted lateral vibration (k31, kp). High frequency (7.5?15 MHz) ultrasonic probes using these ceramics are developed for medical use.