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V Borisov

Publications and source records attributed to V Borisov.

9 recordsLinked to original sources
PubMed2003

The "SCORPION" experiment onboard the International Space Station. Preliminary results.

The "SCORPION" program onboard the Russian Segment (RS) of the International Space Station (ISS) is designed to carry out complex research of the effects of the nar-Earth space parameters on the conditions under which various experiments and operations are being conducted. Special attention in this program was paid to the biological objects onboard the orbital station, e.g. it was found that variation in the number of colony forming units (micromicets and bacteria) correlates with the solar activity and the absorbed dose. The "SCORPION" experiment onboard the RS ISS started in January 2002. It was designed to measure the following parameters inside the space absorbed doses in different places inside the RS ISS, the fluxes of energetic charged particles, neutrons and gamma-quanta; the vectors of the magnetic field and low-frequency electromagnetic waves. At the same time the growth of micromicets on the samples of various materials was studied. The description of the "SCORPION" experiment and the preliminary results obtained onboard the RS ISS in 2002 are presented.

Aspergillus niger↗
PubMed1999

A cytochrome bb'-type quinol oxidase in Bacillus subtilis strain 168.

The aerobic respiratory system of Bacillus subtilis 168 is known to contain three terminal oxidases: cytochrome caa(3), which is a cytochrome c oxidase, and cytochrome aa(3) and bd, which are quinol oxidases. The presence of a possible fourth oxidase in the bacterium was investigated using a constructed mutant, LUH27, that lacks the aa(3) and caa(3) terminal oxidases and is also deficient in succinate:menaquinone oxidoreductase. The cytochrome bd content of LUH27 can be varied by using different growth conditions. LUH27 membranes virtually devoid of cytochrome bd respired with NADH or exogenous quinol as actively as preparations containing 0.4 nmol of cytochrome bd/mg of protein but were more sensitive to cyanide and aurachin D. The reduced minus oxidized difference spectra of the bd-deficient membranes as well as absorption changes induced by CO and cyanide indicated the presence of a "cytochrome o"-like component; however, the membranes did not contain heme O. The results provide strong evidence for the presence of a terminal oxidase of the bb' type in B. subtilis. The enzyme does not pump protons and combines with CO much faster than typical heme-copper oxidases; in these respects, it resembles a cytochrome bd rather than members of the heme-copper oxidase superfamily. The genome sequence of B. subtilis 168 contains gene clusters for four respiratory oxidases. Two of these clusters, cta and qox, are deleted in LUH27. The remaining two, cydAB and ythAB, encode the identified cytochrome bd and a putative second cytochrome bd, respectively. Deletion of ythAB in strain LUH27 or the presence of the yth genes on plasmid did not affect the expression of the bb' oxidase. It is concluded that the novel bb'-type oxidase probably is cytochrome bd encoded by the cyd locus but with heme D being substituted by high spin heme B at the oxygen reactive site, i.e. cytochrome b(558)b(595)b'.

Bacillus subtilis↗
PubMed1999

Magnetic circular dichroism used to examine the interaction of Escherichia coli cytochrome bd with ligands.

The interactions of the fully reduced and fully oxidized cytochrome bd from E. coli with ligands CO, NO, and CN- have been studied by a combination of absorption and magnetic circular dichroism (MCD) spectroscopy. In the reduced cytochrome bd, MCD resolves individual bands due to the high-spin heme b595 and the low-spin heme b558 components of the enzyme, allowing one to separately monitor their interactions along with ligand binding to the heme d component. The data show that at low concentrations, the ligands bind almost exclusively to heme d. At high concentrations, the ligands begin to interact with the low-spin heme b558. At the same time, no evidence for significant binding of the ligands to the high-spin heme b595 is revealed in either the reduced or the fully oxidized cytochrome bd complex. The data support the model [Borisov, V. B., Gennis, R. B., and Konstantinov, A. A. (1995) Biochemistry (Moscow) 60, 231-239] according to which the two high-spin hemes d and b595 share a high-affinity ligand binding site with a capacity for only a single molecule of the ligand; i.e., there is a strong negative cooperativity with respect to ligand binding to these two hemes with cytochrome d having an intrinsic ligand affinity much higher than that of heme b595.

Binding Sites↗
PubMed1997

Spontaneous spectral changes of the reduced cytochrome bd.

Reduction of the membrane-bound cytochrome bd from Bacillus subtilis, Escherichia coli and Azotobacter vinelandii as well as of the purified enzyme from E. coli was followed by secondary absorption changes on a time scale of tens of minutes. The difference absorption spectra of these changes resembled those induced by CO binding with heme d2+ indicating interaction of the heme with an endogenous pi-acceptor ligand. The spontaneous spectral changes were prevented and reversed by CO binding with the reduced cytochrome bd. Bonding of heme d iron to an endogenous protein ligand at the sixth axial position upon reduction is proposed and several possible mechanisms of such a process are considered.

Azotobacter vinelandii↗
PubMed1996

[Intraoperative abdominal echography].

Experience with and the impressions of adopting intraoperative abdominal echography in eighteen patients, aged 26 to 73 years, 9 men and 9 women, are shared. The distribution of patients by pattern of diseases is as follows: colorectal carcinoma--4 cases, liver echinococcus--one, gastric carcinoma--one, hepatocellular carcinoma--one, cholangitis acuta purulenta-one, echinococcus of lung and liver--one, calculous cholecystitis with choledocholithiasis--five, and carcinoma of ductus choledochus--one. Fifty intraoperative abdominal echographies and one intrathoracic supradiaphragmatic echography of the liver are performed. Intraoperative abdominal echography of tumors involving organs of the digestive tract contributes to specify the staging of the neoplastic process. In liver echinococcus it determines precisely the number of cysts and diagnoses impalpable cystic formations, while in choledocholithiasis it documents the presence of calculi in the biliary tracts and eventual dilatation of intrahepatic ones. In five patients intraoperative abdominal echographic is done in conjunction with intraoperative fiber choledochoscopy.

Abdomen↗
PubMed1995

Peroxide complex of cytochrome bd: kinetics of generation and stability.

Hydrogen peroxide reacts with the isolated fully oxidized cytochrome bd from Escherichia coli bringing about spectral changes characterized by increased absorption at 680 nm, disappearance of a charge transfer band at 740 nm and a red shift in the Soret band. Only one type of spectral changes is observed throughout the entire range of H2O2 concentration studied, 5 - 5000 microM. The absorption changes are consistent with peroxide binding to heme d and do not show any evidence for reaction with heme b-595. The spectral response saturates at increased H2O2 concentration with apparent Kd of 30 microM and is reversed by catalase. Stopped-flow measurements show the reaction to be first order with respect to H2O2 with a second order rate constant Kon = 600M-1s-1. Decay of the H2O2-induced spectral changes upon addition of catalase (k approximately 0.001 s-1) is about 20-fold slower than expected for dissociation of peroxide from the complex with heme d assuming a simple reversible binding of H2O2 with Kd and Kon values give above (Koff = Kon). We suggest that the reaction of H2O2 with cytochrome bd may be in fact irreversible, the initial binding followed by a cleavage of the O-O bond and formation of the oxoferryl complex of heme d. Upon removal of excess peroxide, the oxoferryl compound could decay being reduced to the ferric state by endogenous reductants.

Cytochrome b Group↗