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Biomedical subjects

G Gennaro

Publications and source records attributed to G Gennaro.

6 recordsLinked to original sources
PubMed1998

Stopped-flow kinetic studies of low potential electron carriers of the photosynthetic bacterium, Rhodobacter capsulatus: ferredoxin I and NifF.

The kinetics of electron-transfer reactions involving nif-specific proteins from Rhodobacter capsulatus; ferredoxin I, NifF, Fe-protein of nitrogenase and dithionite were studied using stopped-flow spectrophotometry. Kinetic evidence was obtained for the formation of a tight (0.44 microM) complex between NifF and Fe-protein. Under the same conditions, FdI interacted only weakly (Kd > 325 microM) with Fe-protein. There was no evidence for complex formation between NifF and FdI since the reaction NifFSQ + FdIred had a bimolecular rate constant of 12.5 +/- 1.2 x 10(3) M-1 s-1. These results suggest that NifF, which is present in only small quantities in the cell, can make a significant contribution to the overall rate of nitrogen fixation due its high reactivity with Fe-protein. Moreover, the apparent lack of specific interaction between NifF and FdI suggest that they act in vivo in parallel to reduce Fe-protein and not in series.

Dithionite↗
PubMed1996

Cloning, characterization, and regulation of nifF from Rhodobacter capsulatus.

The Rhodobacter capsulatus nifF gene and upstream sequence were cloned by using a probe based on the N-terminal sequence of NifF. nifF was found to not be contained in the previously described nif regions I, II, and III. Comparison of the deduced amino acid sequence showed that it is highly similar to NifF from Azotobacter vinelandii and NifF from Klebsiella pneumoniae. Analysis of translational fusions demonstrated that the regulation of transcription was the same as previously reported at the protein level. Insertional mutagen esis showed that NifF contributes significantly to nitrogenase activity under normal nitrogen-fixing conditions and that it is absolutely required for nitrogen fixation under iron limitation.

Amino Acid Sequence↗
PubMed1996

[Quality control of mammography: potential use of a new device for testing the image quality and the dose].

The authors tested a new equipment containing a phantom to check quality mammographic image and an electronic instrument to measure incident radiation (Phan-EX). The phantom contains objects which have similar characteristics to the details of diagnostic interest and allows an easy and accurate estimation of image quality on the basis of the number of objects detected. The radiation detector, consisting of a solid state photodiode, provides an integer proportional to the input exposure. The results obtained highlighted a good reproducibility of instrument output and a good relationship between these values and the exposure ones obtained with a much more expensive ionization chamber. The device response was linear in varying both the anodic exposure (mAs) and the x-ray tube voltage (varying the energy, the calibration factor varied only by a small percent). The authors conclude that the Phan-EX may be useful for quality assurance of the mammographic unit. Furthermore, they suggest some of its practical applications: daily tests of qualitative of the mammographic unit and the treatment system performance, control of the automatic exposure probe, choice and optimization of exposure and treatment of the film parameters, the determination of the output of the x-ray tube, the evaluation of the sensitivity of different screen/film systems.

Equipment Design↗
PubMed1993

Purification and properties of a nif-specific flavodoxin from the photosynthetic bacterium Rhodobacter capsulatus.

A flavodoxin was isolated from iron-sufficient, nitrogen-limited cultures of the photosynthetic bacterium Rhodobacter capsulatus. Its molecular properties, molecular weight, UV-visible absorption spectrum, and amino acid composition suggest that it is similar to the nif-specific flavodoxin, NifF, of Klebsiella pneumoniae. The results of immunoblotting showed that R. capsulatus flavodoxin is nif specific, since it is absent from ammonia-replete cultures and is not synthesized by the mutant strain J61, which lacks a nif-specific regulator (NifR1). Growth of cultures under iron-deficient conditions causes a small amount of flavodoxin to be synthesized under ammonia-replete conditions and increases its synthesis under N2-fixing conditions, suggesting that its synthesis is under a dual system of control with respect to iron and fixed nitrogen availability. Here we show that flavodoxin, when supplemented with catalytic amounts of methyl viologen, is capable of efficiently reducing nitrogenase in an illuminated chloroplast system. Thus, this nif-specific flavodoxin is a potential in vivo electron carrier to nitrogenase; however, its role in the nitrogen fixation process remains to be established.

Amino Acids↗