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Biomedical subjects

D W Krogmann

Publications and source records attributed to D W Krogmann.

At least 37 records · Page 2Linked to original sources
PubMed1979

Isolation of photosynthetic catalysts from cyanobacteria.

Methods are described for the isolation of ferredoxins I and II, cytochrome c-553, cytochrome f, cytochrome c-550 and plastocyanin from large quantities of various cyanobacteria. The amino acid composition of cytochrome c-550 is reported. There is a variation in the relative amounts of these proteins in different batches of cells which may relate to the nutritional status of the organisms.

Amino Acids↗
PubMed1975

Mechanism of KCN inhibition of photosystem I.

Experiments with chloroplasts and purified spinach plastocyanin suggest a mechanism for KCN inhibition of Photosystem I. KCN inhibition can be bypassed by a detergent or reversed by replacement of the inactive plastocyanin. KCN bleaches and inactivates purified plastocyanin. KCN releases copper from chloroplast membranes and from purified plastocyanin. Cyanide does not bind to the apoprotein produced when plastocyanin is treated with KCN, and KCN-produced apoplastocyanin has a N-ethylmaleimide-reactive sulfhydryl group not found in holoplastocyanin. Apoplastocyanin is not active in restoring Photosystem I activity to plastocyanin-depleted membranes. Holoplastocyanin restores Photosystem I activities to plastocyanin-depleted membranes prepared from either control or KCN-treated chloroplasts to about the same extent. KCN-treated chloroplast membranes are found to have higher amounts of apoplastocyanin than do control chloroplast membranes. These results offer evidence that KCN removes the copper from plastocyanin in the chloroplast membrane, leaving the inactive apoplastocyanin which is unable to transfer electrons to Photosystem I.

Chloroplasts↗
PubMed1975

Nuclear magnetic resonance studies of the copper binding sites of blue copper proteins: oxidized, reduced, and apoplastocyanin.

Proton nuclear resonance spectra at 250 MHz of plastocyanins from spinach (Spinacia oleracea) and a blue green alga (Anabaena variabilis) are reported. Spectra of the reduced plastocyanins contain well-resolved peaks from slowly exchangeable N-H, histidine C2-H tyrosine ring, peptide alpha-CH, and high-field protons. The widths of these peaks indicate that the plastocyanins are monomeric. When the plastocyanins are oxidized, several changes in the spectra are observed including disappearance of peaks assigned to two histidine side chains. The pKa' values of the two histidine residues of reduced spinach plastocyanin are abnormally low (4.9 and less than 4.5). These pKa' values become more normal in apoplastocyanin or plastocyanin inhibited by cyanide. The results suggest that the imidazole groups of the two histidine residues are liganded directly to the copper in plastocyanin. The displacement of copper by cyanide is reversed at low pH. Spectra of apo- and reduced plastocyanins show only minor differences. However, the slowly exchangeable protons of plastocyanin exchange more rapidly in the apoprotein. Copper binding apparently does not cause a major reorganization of the protein structure, but the presence of copper does stabilize this structure.

Apoproteins↗
PubMed1975

Polycation interactions with spinach ferredoxin-nicotinamide adenine dinucleotide phosphate reductase.

Polylysine stimulates the activity of ferredoxin-NADP reductase. The stimulation is observed with three different catalytic activities of this enzyme. The stoichiometry of interaction of polylysine and enzyme is a function of the size of the polylysine molecule. Polylysine alters the absorption and fluorescence emission spectra of the enzyme with the same stoichiometry as that affecting catalytic activity. Steady state initial velocity kinetics indicates that polylysine is a noncompetitive hyperbolic activator of the enzyme and is able to prevent substrate inhibition by NADPH. In the absence of polylysine, the specific activity of the enzyme increases upon dilution, and this effect is magnified in the presence of polylysine. These results suggest that the soluble enzyme is an aggregate, and gel filtration measurements indicate a molecular weight of 85,000 for the purified enzyme, which appears to consist of two subunits. This confirms the observations of Fredricks and Gehl (FREDRICKS, W. W., AND GEHL, J. M. (1973) Fed. Proc. 32, 477). Indirect evidence is presented suggesting the enzyme is bound to a cationic region on the chloroplast membrane.

2,6-Dichloroindophenol↗
PubMed1974

Chloroplast grana membrane carboxyl groups: their involvement in membrane association.

Chloroplast membrane carboxyl groups were modified by carbodiimide activation followed by glycine methyl ester substitution, leaving the derivatized group uncharged. This charge alteration induced a number of effects similar to addition of salts to control chloroplasts suspended in a low salt medium. These include: (a) restacking or multiple membrane association in low salt-treated chloroplasts that lack grana stacks, (b) protection against polycation inhibition of photosystem I electron transfer, (c) reduction of the amount of polycations bound to the membranes, and (d) increased 90 degrees light scattering due to membrane conformational changes. Carboxyl modification also altered acid-induced conformational changes.These effects are interpretated as the results of the reduction in the surface negative charge contributed by carboxyl groups. Membrane structure at both a local, polyelectrolyte level and at the level of membrane-membrane interaction (stacking) is controlled in part by these negative, charged groups.

Journal Article↗
PubMed1972

Inhibition of chloroplast reactions with phenylmercuric acetate.

Phenylmercuric acetate is a selective inhibitor of the photosynthetic activities of isolated spinach (Spinacia oleracea) chloroplasts. At 5 mum concentration of phenylmercuric acetate, photophosphorylation is inhibited. At 33 mum phenylmercuric acetate, ferredoxin is inactivated. Ferredoxin-NADP oxidoreductase is 50% inhibited at 100 mum phenylmercuric acetate. Photosystem II reactions are 50% inhibited at 150 mum phenylmercuric acetate and very much higher cooncentrations-500 mum-are needed to approach complete inhibition. Phenylmercuric acetate inhibition of photosystem II appears to be selective, blocking a site between the 3-(3,4-dichlorophenyl)-1,1-dimethyl urea sensitive site and the site inactivated by high concentrations of tris buffer.

Journal Article↗
PubMed1971

A Lipid Requirement for Photosystem I Activity in Heptane-extracted Spinach Chloroplasts.

A lipid requirement for photosystem I activity in Spinacia oleracea chloroplasts has been characterized. The transfer of electrons from tetramethyl-p-phenylenediamine through the chloroplast photosystem to viologen dye was used as an assay of photosystem I activity. Activity is diminished by prolonged heptane extraction and is partially restored by readdition of the extracted lipid. Extracted chloroplasts require plastocyanin for maximal restoration of activity. The effect of lipid extract in restoration is partially replaced by triglycerides containing unsaturated, C(18) fatty acids. Various potential redox carriers which occur naturally in chloroplasts do not substitute for extracted lipid. Galacto-lipids, sulfolipids, and phospholipids are not involved in the restoration of activity.

Journal Article↗