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The e¡ects of glycerol and high temperatures on structure and function of phycobilisomes (PBSs) in vivo were investigated in a chlL deletion mutant of the cyanobacterium Synechocystis sp. PCC 6803. When the mutant was grown under light-activated heterotrophic growth conditions, it contained intact and functional PBSs, but essentially no chlorophyll and photosystems. So the structural and functional changes of the mutant PBSs in vivo can be handily detected by measurement of low temperature (77 K) £uorescence emission spectra. High concentration glycerol induced an obvious disassembly of PBSs and the dissociation of phycocyanins in the rod substructures into their oligomers and monomers. PBSs also disassembled at high temperatures and allophycocyanins were more sensitive to heat stress than phycocyanins. Our results demonstrate that the chlL 3 mutant strain is an advantageous model for studying the mechanisms of assembly and disassembly of protein complexes in vivo. ß

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SummaryInactivation of the chlL gene in Synechocystis sp. PCC 6803 resulted in negligible chlorophyll content when the mutant was grown in darkness. Upon phycocyanin excitation at 580 nm, the 77K uorescence spectrum of dark-grown cells showed three peaks at 648 nm, 665 nm, and 685 nm, this last being the largest. This re ects the functional presence of major components of phycobilisomes, including phycocyanin, allophycocyanin, and the terminal emitter, and ef cient energy transfer between these components. As expected, no uorescence emission peaks corresponding to chlorophyll in the photosystems were observed. Intact phycobilisomes could be isolated from the dark-grown chlL-deletion mutant. However, the phycobilisomes had a lower ef ciency of energy transfer than did those isolated from the light-grown mutant, probably because of a decreased phycobilisome stability in the absence of chlorophyll. Exposing the dark-grown chlL-deletion mutant to light triggered the biosynthesis of chlorophyll. For the rst 6 h in the light, upon phycocyanin excitation at 580 nm, the 77K uorescence emission spectrum of greening cells was identical to that of dark-grown cells that lacked signi cant amounts of chlorophyll. With increased chlorophyll synthesis, gradual energy transfer from phycobilisomes to the two photosystems can be demonstrated. IUBMB Life, 48: 625-630, 1999

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The increase of the protein transition enthalpy upon adsorption onto biomedical material surfaces was observed by measuring the differential scanning calorimetry (DSC) traces of bovine fibrinogen adsorbed onto a hydroxyapatite surface. The mechanism causing the transition enthalpy increase upon adsorption was clarified by using DSC measurements of bovine fibrinogen for different ionic strength and sodium dodecyl sulfate concentrations. The results suggest that the increased fibrinogen transition enthalpy may be attributed to the electrostatic interactions between the carboxyl of the D domains and the calcium loci ofhydroxyapatite, which may result in a more compact protein structure

Changes in the protein secondary structure and electron transport activity of the Triton X-100-treated photosystem I (PSI) and photosystem II (PSII) complexes after strong illumination treatment were studied using Fourier transform-infrared (FT-IR) spectroscopy and an oxygen electrode. Short periods of photoinhibitory treatment led to obvious decreases in the rates of PSI-mediated electron transport activity and PSII-mediated oxygen evolution in the native or Triton-treated PSI and PSII complexes. In the native PSI and PSII complexes, the protein secondary structures had little changes after the photoinhibitory treatment. However, in both Triton-treated PSI and PSII complexes, short photoinhibition times caused significant loss of alpha-helical content and increase of beta-sheet structure, similar to the conformational changes in samples of Triton-treated PSI and PSII complexes after long periods of dark incubation. Our results demonstrate that strong-light treatment to the Triton-treated PSI and PSII complexes accelerates destruction of the transmembrane structure of proteins in the two photosynthetic membranes.

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