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Biomedical subjects

D S Berns

Publications and source records attributed to D S Berns.

At least 37 records · Page 2Linked to original sources
PubMed1981

Thermodynamics of carbohydrate-lipid interactions.

Thermodynamic analyses of carbohydrate-lipid interactions were performed by investigating the effects of a series of carbohydrates, including monosaccharides, disaccharides, and trisaccharides, on the phase-transition properties of aqueous dispersions of 1,2-dipalmitoyl phosphatidylcholine (DPPC). The temperature of the lipid's main phase transition from the gel to liquid-crystalline phase is essentially unchanged in the presence of carbohydrate. The change in the free energy (delta G) of the transition is zero when a carbohydrate is added to aqueous dispersions of DPPC, while the enthalpy (delta H) and the entropy of the melting of DPPC are decreased. The thermodynamic information was used to examine carbohydrate-lipid interactions. Such interactions were elucidated according to our knowledge of the specific properties of carbohydrates in aqueous solutions and the previously proposed hydrophobic interaction involving hydrocarbon tails of the lipid in aqueous dispersions.

Calorimetry, Differential Scanning↗
PubMed1981

Accumulation of protoporphyrin IX and Zn protoporphyrin IX in Cyanidium caldarium.

In vivo fluorescence studies of Cyanidium caldarium mutants grown in the dark in dextrose-containing media have shown that these organisms accumulate protoporphyrin IX. In the dark the accumulated protoporphyrin IX is gradually turned into a metalloporphyrin, Zn protoporphyrin. In the light, in the chlorophyll-lacking mutant GGB, both compounds are degraded and phycobiliproteins are formed. These results implicate protoporphyrin IX in situ as the general precursor to tetrapyrrole pigments and Zn protoporphyrin IX as a possible intermediate or regulator in the biosynthesis of phycobilins.

Journal Article↗
PubMed1980

Chromophore interactions in allophycocyanin.

Allophycocyanin, which is normally isolated as a trimer (alpha 3 beta 3), has now been successfully dissociated into a monomer (alpha beta) with strikingly different spectroscopic properties. In particular, upon dissociation the characteristic 650-nm absorption and 661-nm fluorescence emission bands of the trimer are completely lost and its fluorescence polarization properties are sharply altered. The spectroscopic characteristics of allophycocyanin monomers are much closer to those of C-phycocyanin than to trimeric allophycocyanin. A model for trimeric allophyocyanin is presented in which the appearance of the 650-nm absorption band is induced by a particular kind of chromophore-chromophore interaction. Similar results are found for both allophycocyanin II and III.

Cyanobacteria↗
PubMed1980

Thermotropic Properties of Thermophilic, Mesophilic, and Psychrophilic Blue-green Algae.

Thermotropic properties of blue-green algae grown at high, room, and low temperatures in H(2)O and D(2)O media were studied by highly sensitive differential scanning microcalorimetry. The thermograms of these organisms contain an endothermal peak in the temperature range of 50 to 70 C with an endothermal heat ranging from 0.14 to 1.91 joules per gram organism. The temperature at which the endothermal peak occurs is comparable with the thermal denaturation temperature of phycocyanin, the major biliprotein isolated from these algae. A good correlation can be found for the relative thermal stability of various organisms with that of the isolated biliproteins. The ability of these algae to resist thermal disruption is correlated with the thermal environments in which these algal cells grow. The thermal stability of normal algae is in the order of thermophile > mesophile > psychrophile. It was found that the deuterated mesophilic algae were less able to resist thermal disruption than ordinary mesophilic algae.

Journal Article↗
PubMed1979

Energy transfer among the chromophores in phycocyanins measured by picosecond kinetics.

Energy-transfer processes in the algal light-harvesting proteins, the phycocyanins, have been studied by means of picosecond absorption spectroscopy. After excitation at 530 nm, the absorption at several wavelengths in the range 480--669 nm decayed with a short time constant (picosecond) and a long time constant (greater than 1 ns). For C-phycocyanin, energy transfer from the beta to the alpha subunits is interpreted as being a likely candidate for the short time constant; the long time constant probably is the excitation lifetime of the chromophore on the alpha subunits. The time constants for energy transfer in monomers, trimers, and hexamers of C-phycocyanin extracted from a blue-green alga, Phormidium luridum, were measured as approximately 85, approximately 56, and approximately 32 ps, respectively. The corresponding time constant in the cryptomonad phycocyanin 645 from Chroomonas species was found to be less than 5 ps.

Cyanobacteria↗
PubMed1979

Effect of plastocyanin and phycocyanin on the photosensitivity of chlorophyll-containing bilayer membranes.

Photovoltaic effects were studied in bilayer membranes constructed from phosphatidyl choline, monogalactosyl diglyceride, chlorophyll alpha and beta-carotene. It was demonstrated that the biliprotein C-phycocyanin enhanced the photosensitivity of these membranes. Plastocyanin, an important photosynthetic electron transfer protein, was also found to be effective in enhancing the membrane photovoltage. The C-phycocyanin and plastocyanin were effective on opposite sides of the membrane. Plastocyanin operates to transfer electrons into the membrane, while C-phycocyanin directs electron transfer from the membrane. Membranes containing monogalactosyl diglyceride were found to be extremely stable and were most susceptible to enhancement of photosensitivity by introduction of the proteins. The plastocyanin and C-phycocyanin when used together appeared to operate synergistically.

Carotenoids↗
PubMed1979

Psychrophile C-phycocyanin.

C-Phycocyanin was purified from an alga isolated in the Antarctic in 1968 and grown since that time in our laboratory at 4 C. Certain of its spectroscopic and immunochemical properties were studied, along with detailed examinations of its chemical composition and quaternary structure. The hexamer-trimer equilibrium in the protein solution was studied as a function of pH, ionic strength, temperature, and susceptibility to certain small molecules. A major emphasis of the work was placed on a comparison of its protein-protein interactions with those of C-phycocyanins from both mesophilic and thermophilic algae.

Journal Article↗
PubMed1978

Comparison of the stability of phycocyanins from thermophilic, mesophilic, psychrophilic and halophilic algae.

Protein unfolding of eight different phycocyanins was investigated utilizing circular dichroism and visible spectra. The phycocyanin samples were extracted from algae that are normally found in vastly different environments, and are classified as mesophilic, thermophilic, halophilic and psychrophilic. The ability of these proteins to resist the denaturant urea is in the order of thermophile greater than mesophile, halophile greater than psychrophile. Based on a two-state approximation the apparent free energies of protein unfolding at zero urea denaturant concentration, deltaGH2Oapp, were found to range from 2.4 to 8.8 kcal/mole for the eight phycocyanins at pH 6 and 25 degrees C. The proteins from the thermophile are generally more stable than those from the mesophile. An extra stability of the halophile is believed due to the specific interaction of the proteins and the ions in solution. A correction for deltaGH2Oapp due to minor amino acid differences reveals that the stability and the structural properties of these proteins are primarily affected by this minor difference in amino acid compositions.

Amino Acids↗
PubMed1977

Denaturation of phycocyanin by urea and determination of the enthalpy of denaturation by microcalorimetry.

Denaturation of the protein phycocyanin in urea solution was investigated by microcalorimetry, ultraviolet and visible spectroscopy, circular dichroism and sedimentation equilibrium. The results consistently demonstrated that in the presence of 7 M urea this protein is completely denatured. By assumings a two-state mechanism, an apparent free energy of unfolding at zero denaturant concentration, (formula: see text) was found to be 4.4 kcal/mole at pH 6.0 and 25 degrees C. By microcalorimetry the enthalpy of denaturation of phycocyanin app was found to be -230 kcal/mole at 25 degrees C. The relatively large negative enthalpy change results from protein unfolding and changes in protein solvation.

Binding Sites↗
PubMed1977

Similar C-phycocyanins from two strains of thermotolerant cyanophyte Mastigocladus laminousus.

C-phycocyanin from two strains of the thermotolerant blue-green alga, Mastigocladus laminosus (NZ-DB2-m and I-30-m), that grow within different temperature ranges have been characterized with respect to aggregation, immunologic properties, subunit composition, and thermodenaturation. The critical thermal-denaturation temperature for phycocyanin from both strains of M. laminosus phycocyanin is 60 degrees C which is higher than that for mesophilic phyococyanin. Immunodiffusion studied have shown that these two strains of M. laminosus exhibit no antigenic differences and are closely related to the mesophilic Plectonema calothricoides and the thermophilic Synechococcus lividus (strains 3). Neither phenol nor alpha-naphthol has any effect on phycocyanin aggregation in these two strains of M. laminosus. There is also no enhancement of formation of large aggregates at their elevated temperature of cultivation. Furthermore, the phycocyanin of both strains of M. laminosus does not demonstrate any large amount of 19S or higher aggregates at any pH value. These observations suggest that the mode of adaptation of M. laminosus phycocyanin to high temperature is differnet from the previously encountered. It is also important to note that phycocyanin is essentially unchanged whether it is extracted from the same strain, M. laminosus (NZ-DBS-m), grown at either 50 degrees C or 37 degrees C.

Adaptation, Biological↗
PubMed1975

Letter: Sequences of the N-terminus portions of biliproteins.

The N-terminal sequences of the separated polypeptide chains of biliproteins isolated from several Cyanophyta, Rhodophyta, and Cryptophyta have been determined. The portions of the sequences determined for the alpha (fast) chain of C-phycocyanin from both procaryotic and eucaryotic cells are extremely conservative. Methionine is the N-terminal amino acid in most of the species studied. The N-terminus and subsequent sequence of phycoerythrin alpha chains are almost identical with those of the C-phycocyanin alpha chain. The beta (slow) chain of C-phycocyanin is also rather conservative in amino acid substitution but has more variation than the alpha chain. The variations are consistent with single base changes in codons and conserve the size and functional characteristics of the amino acid. The sequence homologies are consistent with the phylogenetic relationship between Cyanophyta and the chloroplast of Rhodophyta. There are no other reported sequences of polypeptide chains of the same or related proteins from such different strains of microorganisms that show such close sequence homology.

Amino Acid Sequence↗
PubMed1975

Dependence of photosensitivity of bileaflet lipid membranes upon the chlorophyll and carotenoid content.

Bileaflet lipid membranes were formed from solutions containing lecithin, chlorophyll and carotene in various concentrations. If all the above components were present at sufficient concentrations the membranes were photosensitive; i.e., a photocurrent was produced if a redox potential gradient was present across the membranes. The presence of chlorophyll and carotene were essential for the photosensitivity of the membranes. Photoresponse could be elicited by illuminating the membrane with light which did not excite carotene. On the other hand, elimination of the part of the light spectrum which excites chlorophyll led to the abolition of the photoresponse. The findings of this study are consistent with the assumption that the excited chlorophyll chromophores allow electron exchange at the membrane-water interface while the presence of carotene allows electron movement across the "bulk" lipid membrane.

Binding Sites↗
PubMed1975

Physical-chemical properties of C-phycocyanin isolated from an acido-thermophilic eukaryote, Cyanidium caldarium.

C-Phycocyanin from an acido-thermophilic eukaryotic alga, Cyanidium caldarium, was characterized with respect to subunit structure, absorption spectrum and fluorescence properties and was found to be similar to C-phycocyanins from mesophilic sources. The pH-dependence of fluorescence polarization and the changes in sedimentation velocity as a function of pH, concentration and temperature indicate the presence of extremely large amounts of unusually stable 19S aggregates. It was not possible to disaggregate this phycocyanin completely to monomer under normal conditions. The amino acid composition is similar to that of phycocyanins from other thermophilic and halophilic sources. The isoelectric point of this C-phycocyanin was 5.11, an unusually high value. The properties of this C-phycocyanin suggest an increase in protein stability as its mode of adaptation to the environmental stress of high temperature.

Amino Acids↗