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Biomedical subjects

D S Berns

Publications and source records attributed to D S Berns.

At least 55 records · Page 3Linked to original sources
PubMed1975

Modification of intensity and direction of electron flow across bileaflet membranes.

The intensity and the direction of electron flow across chloroplast extract bilayer membranes are modified by the presence of biliproteins. Biliproteins including C-phycocyanin, phycoerythrin, allophycocyanin, and Chroomonas phycocyanin enhance the photosensitivity of the membranes. The photoelectric spectra of the membranes in the presence of biliproteins correlate with the absorption spectra of these biliproteins. Experiments are presented to demonstrate the specific character of the electron-directing ability of biliproteins. A possible mechanism involving the interaction between the biliproteins and the membranes is proposed.

Cell-Free System↗
PubMed1974

Comparison of the biliproteins from two strains of the thermophilic cyanophyte Synechococcus lividus.

C-Phycocyanins from two thermophilic strains of Synechococcus lividus that grow within different temperature ranges have been shown to be unalike. The aggregation ability of these two C-phycocyanins in sedimentation-velocity experiments varied dramatically. Surprisingly, the aggregation properties of mesophilic C-phycocyanins were found to lie between those of the two thermophilic proteins. Under identical conditions at pH7.0, one thermophilic protein (Sy I) was composed of 17S and larger aggregates, whereas the other (Sy III) was an almost homogeneous 6S aggregate. Mesophilic C-phycocyanins have a mixture of 6S, 11S and less stable 17S aggregates under these conditions. Amino acid analysis, absorption spectra, immunochemistry and fluorescence polarization all indicated differences in the composition and properties of the thermophilic proteins, which suggest that they have different modes of adaptation to very high temperatures. Allophycocyanins from the two strains of S. lividus were also purified and studied, but unlike the C-phycocyanins no major differences were found between them. Allophycocyanin was homogeneous at pH6.0, with a sedimentation coefficient of 5.54S and mol.wt. 1.03x10(5), as determined by sedimentation-equilibrium measurements.

Amino Acids↗
PubMed1973

The characterization of C-phycocyanin from an extremely halo-tolerant blue-green alga, Coccochloris elabens.

C-Phycocyanin was isolated and purified from a uni-algal culture of an extremely halo-tolerant blue-green alga, Coccochloris elabens. This alga can be grown under laboratory conditions in 25% (w/v) NaCl. Purified halophile phycocyanin was characterized by amino acid analysis and the measurement of sedimentation velocity, fluorescence polarization and immunodiffusion as a function of protein concentration, pH and ionic strength. The results were compared with those of studies of phycocyanin isolated from Plectonema calothricoides and from several other sources. The states of aggregation previously characterized as being present in other C-phycocyanins, monomer, trimer and hexamer, were present in halophile phycocyanin and were characterized as antigenically related to all C-phycocyanins tested. The equilibrium between 3S monomer and 11S hexamer at low concentrations in halophile phycocyanin was quantitatively similar to that for other phycocyanins. The effect of pH and ionic strength on the 6S (trimer) and 11S (hexamer) aggregation of halophile phycocyanin was markedly salt-dependent and the relative amount of each aggregate in the presence of 2m-NaCl was like that of C-phycocyanin from mesophiles, in the absence of additional salt. In antigenic relationship and aggregation properties, the phycocyanin from C. elabens appeared to be most closely related to that isolated from the thermophilic blue-green alga, Synechococcus lividus. Amino acid content of the halophile phycocyanin indicated the presence of a significantly larger number of acidic residues than that found in mesophiles. Explanations of the properties of the halophile protein require consideration of a strong contribution of hydrophobic forces and utilize both charge-shielding and salting-out effects.

Amino Acids↗
PubMed1971

Protein aggregation in C-phycocyanin. Studies at very low concentrations with the photoelectric scanner of the ultracentrifuge.

Solutions of C-phycocyanin of very low concentrations were examined by sedimentation-velocity studies in the Spinco model E ultracentrifuge equipped with a photoelectric scanning system and a monochromator. At sufficiently low concentrations complete disaggregation from the hexamer to the monomer was observed. The equilibrium constant of monomer to hexamer was estimated to be approx. 10(30). For studies of aggregation over the complete range of concentration, C-phycocyanins from Phormidium luridum and Lyngbya sp. were used. Sedimentation-velocity studies at high concentration with schlieren optics are reported for C-phycocyanins from Anabaena variabilis and Lyngbya sp. The pH-dependence of aggregation and the temperature-dependence of trimer-hexamer equilibrium for phycocyanins from these algae were found to be similar to those of other C-phycocyanins. The principal feature of the pH-dependence is the dominance of hexamers at the isoelectric point. Increasing temperature increased the amount of hexamer and decreased the amount of trimer.

Centrifugation, Density Gradient↗