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R Malkin

Publications and source records attributed to R Malkin.

At least 91 records · Page 5Linked to original sources
PubMed1975

Laser-flash-activated electron paramagnetic resonance studies of primary photochemical reactions in chloroplasts.

Electron paramagnetic resonance studies of the primary reactants of Photosystems I and II have been conducted at cryogenic temperatures after laser-flash activation with monochromatic light.P-700 photooxidation occurs irreversibly in chloroplasts and in Photosystem I fragments after activation with a 730 nm laser flash at a temperature of 35 degrees K. Flash activation of chloroplasts or Photosystem II chloroplast fragments with 660 nm light results in the production of a free-radical signal (g = 2.002, linewidth approximately 8 gauss) which decays with a half-time of 5.0 ms at 35 degrees K. The half-time of decay is independent of temperature in the range of 10-77 degrees K. This reversible signal can be eliminated by preillumination of the sample at 35 degrees K with 660 nm light (but not by 730 nm light), by preillumination with 660 nm light at room temperature in the presence of 3-(3',4'-dichlorophenyl)-1,1'-dimethylurea (DCMU) plus hydroxylamine, or by adjustment of the oxidation-reduction potential of the chloroplasts to - 150 mV prior to freezing. In the presence of ferricyanide (20-50 mM), two free-radical signals are photoinduced during a 660 nm flash at 35 degrees K. One signal decays with a half-time of 5 ms, whereas the second signal is formed irreversibly. These results are discussed in terms of a current model for the Photosystem II primary reaction at low temperature which postulates a back-reaction between P-680+ and the primary electron acceptor.

Ascorbic Acid↗
PubMed1974

The isolation and characterization of a new iron-sulfur protein from photosynthetic membranes.

A new iron-sulfur protein, distinct from the soluble chloroplast ferredoxin, was isolated from chloroplast membranes. The isolated protein, purified to homogeneity, had a molecular weight of about 8000 and 4 atoms of iron and 4 inorganic sulfides per mole. Its absorption spectrum had a broad absorbance band in the 400 nm region, a shoulder at approximately 310 nm, and a peak around 280 nm. The absorbance ratio A(400) to A(280) was 0.55. The electron paramagnetic resonance spectrum (measured at 12 degrees K) of the reduced protein was similar to that of other reduced iron-sulfur proteins, showing a major resonance line at g = 1.94. The isolated protein, when photoreduced by spinach chloroplasts, can in turn transfer electrons to mammalian cytochrome c. However, the photoreduced protein cannot replace soluble ferredoxin in NADP(+) reduction because of its apparent inability to interact with the chloroplast enzyme, ferredoxin-NADP(+) reductase. The relation of the isolated iron-sulfur protein to the bound ferredoxin that acts as the primary electron acceptor in Photosystem I is discussed.

Chloroplasts↗