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Biomedical subjects

A S Pietro

Publications and source records attributed to A S Pietro.

18 recordsLinked to original sources
PubMed1985

Effect of Ferredoxin on the Diaphorase Activity of Cyanobacterial Ferredoxin-NADP Reductase.

The interaction of ferredoxin-NADP reductase (FNR) and ferredoxin (Fd) results in an enhanced rate of reaction and a shift of the pH optimum for the FNR-mediated diaphorase reaction. Low concentrations of NaCl (<100 millimolar), favorable for formation of the FNR:Fd complex, further magnify the alteration of the diaphorase reaction; the activity is enhanced 3-fold and pH optimum is shifted from 9.5 to 7.8. The Fd-stimulated diaphorase activity of FNR may result either from a conformational change of the enzyme and/or from a transition from a two electron to a one electron reaction.

Journal Article↗
PubMed1980

Electron donation to photosystem I.

Electron donation to photosystem I was studied in highly resolved particles from spinach. Divalent cations increased the efficiency of electron donation from spinach plastocyanin to P700(+) through a decrease in the apparent K(m) for plastocyanin. Cytochrome f was not an efficient electron donor for P700(+) in the presence or absence of divalent cations. Cytochrome f photooxidation could be observed in the presence of both plastocyanin and divalent cations.The efficiencies of electron donors from eukaryotic and prokaryotic algae to P700(+) were also examined. Divalent cations enhanced the effectiveness of electron donors from eukaryotic organisms, while inhibiting electron donors from prokaryotic organisms. The prokaryotic electron donors were also much more efficient donors than were the electron donors from eukaryotic organisms. A correlation between the K(m) for the electron donor and its isoelectric point suggests that the net charge on the donor protein is a major determinant of the efficiency for electron donation. The data presented raise interesting questions with respect to the evolution of electron donation to photosystem I and the possibility of an additional electron carrier between plastocyanin and P700(+).

Journal Article↗
PubMed1975

Partial Reactions of Photosynthesis in Briefly Sonicated Chlamydomonas: II. Photophosphorylation Activities.

Briefly sonicated Chlamydomonas reinhardi cells are capable of both cyclic and noncyclic photophosphorylation and, in each case, the maximum rates approach those reported for higher plant chloroplasts. Photophosphorylation coupled to ferricyanide reduction occurs with a P/2e ratio approaching unity.The conditions for optimum activity are similar to those reported for spinach or swiss chard chloroplasts; the major difference is the extreme sensitivity to salt and relative insensitivity to methylamine. Cell preparation, sonication, and assays were all performed at room temperature under conditions suitable for screening a large number of potential mutants deficient in photophosphorylation activity. This method was easily adapted to Euglena gracilis strain Z but not adaptable for Chlorella vulgaris or Scenedesmus obliquus strain D(3).

Journal Article↗
PubMed1971

Proton magnetic resonance studies of the ferredoxins from spinach and parsley.

Contact-shifted resonances have been detected in the pmr spectra of both oxidized and reduced forms of spinach and parsley ferredoxins. These resonances are assigned to the beta-CH(2) protons of four cysteine residues that are thought to bind the iron-sulfur redox center to the polypeptide chain. Temperature dependences of contact shifts reveal that the two iron atoms are antiferromagnetically coupled in both redox forms of each of these proteins. Thermal population of magnetic states gives rise to the contact shifts observed in the formally diamagnetic oxidized forms of these ferredoxins and accounts for the failure of contact shifts in the reduced forms exhibit to a Curie Law temperature dependence. It appears that the unpaired electron of reduced spinach and parsley ferredoxin is unequally distributed over the two iron centers. Valence states for the iron pairs of high-spin Fe(+3)-Fe(+3) and Fe(+2)-Fe(+3) for the oxidized and reduced forms, respectively, are compatible with the nmr results.

Electron Spin Resonance Spectroscopy↗