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PubMed1994

Threshold and chromatic sensitivity changes in fish cone horizontal cells following prolonged darkness.

The light-evoked responses of L-type cone horizontal cells in the teleost retina were studied following a prolonged period of complete darkness. Intact, isolated white perch retinas were superfused in complete darkness for more than 90 min, following which horizontal cells were impaled without the aid of any light flashes. Following this prolonged darkness, L-type cone horizontal cell light responses to dim and bright full-field stimuli were slow and small in amplitude and response duration to bright stimuli was considerably longer than stimulus duration. In addition, absolute threshold was 2 log units lower than typical for cone horizontal cells and spectral sensitivity to shorter wavelengths was increased. Following bright light stimulation, light responses became more transient and increased in amplitude, reaching 40-50 mV to bright flashes. Moreover, absolute threshold increased and responses to spectral stimuli were similar to those observed typically for L-type cone horizontal cells after light-sensitization. These results suggest that following prolonged darkness, cone input to cone horizontal cells is reduced and rod input is present.

Animals↗
PubMed1991

Isolation, crystallization, crystal structure analysis and refinement of constitutive C-phycocyanin from the chromatically adapting cyanobacterium Fremyella diplosiphon at 1.66 A resolution.

Constitutive phycocyanin from cyanobacterium Fremyella diplosiphon (Calothrix sp. PCC 7601) grown in green light, has been isolated and crystallized. The crystals belong to the space group R3 with cell constants a = b = 180.26 A, c = 61.24 A, alpha = beta = 90 degrees, gamma = 120 degrees. The crystal structure has been determined by Patterson search techniques using the molecular model of C-phycocyanin from the cyanobacterium Agmenellum quadruplicatum. The asymmetric unit of the crystal cell consists of two (alpha beta)-monomers related by a local dyad. Three asymmetric units are arranged around a crystallographic triad and form an (alpha beta)6-hexamer, the functional unit in the native antenna rod. The initial structure has been refined in a cyclic manner by energy-restrained crystallographic refinement and modelling until the conventional crystallographic R-factor converged at 18.1% with data to a resolution of 1.66 A. The molecular structure resembles closely the C-phycocyanins of Mastigocladus laminosus and A. quadruplicatum. The conformation and configuration of the alpha-84 and beta-84 chromophores is very similar to the corresponding chromophores in the trimeric C-phycocyanin of M. laminosus, whereas the beta-155 chromophore differs in configuration with C(4)-Z, C(10)-Z and C(15)-Z compared to C(4)-Z, C(10)-Z, C(15)-Z,E. The stereochemistry of the beta-155 chiral centres is C(2)-RC(3)-R and C(31)-S, respectively, whereas alpha-84 and beta-84 have C(2)-RC(3)-R and C(31)-R. The amino acid sequences of constitutive and inducible phycocyanin differ mainly in residues located on the surface of the beta-subunits that mediate the inter-hexameric contacts.

Amino Acid Sequence↗
PubMed1982

Thiourea prevents cytotoxicity and mutagenicity, but not sister-chromated exchanges in V79 cells treated with cis-diaminedichloroplatinum (II).

This work shows that cis-diaminedichloroplatinum(II)'s (cis-DDP) mutagenicity, as well as its cytotoxicity, can be prevented by subsequent treatment with thiourea. Sister-chromatid exchanges (SCE) induced by cis-DDP are only partially prevented by thiourea under conditions where mutagenicity is totally inhibited. A 4.5-h delay in the addition of thiourea following cis-DDP treatment results in an almost complete loss of its ability to prevent mutagenicity, but only a partial loss of its ability to prevent cytotoxicity and sister-chromatid exchanges.

Animals↗