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Biomedical subjects

S Silver

Publications and source records attributed to S Silver.

At least 163 records · Page 9Linked to original sources
PubMed1977

Mercury and organomercurial resistances determined by plasmids in Staphylococcus aureus.

Penicillinase plasmids of Staphylococcus aureus often contain genes conferring resistance to inorganic mercury (Hg(2+)) and the organomercurial phenylmercury acetate. The mechanism of resistance was found to be the enzymatic hydrolysis of the organomercurial phenylmercury to benzene plus inorganic ionic mercury, which was then enzymatically reduced to metallic mercury (Hg(0)). The Hg(0) was rapidly volatilized from the medium into the atmosphere. After the mercurial was degraded and the mercury was volatilized, the resistant cells were able to grow. These plasmids also conferred the ability to volatilize mercury from thimerosal, although the plasmid-bearing strains were equally as thimerosal sensitive as the S. aureus without plasmids. None of the plasmids conferred the ability to volatilize mercury from several other organomercurials, however: methylmercury, ethylmercury, p-hydroxymercuribenzoate, merbromin, and fluorescein mercuric acetate. (Organomercurial resistance-conferring plasmids of Escherichia coli and Pseudomonas aeruginosa that we have been studying confer the ability to degrade two or three of these organomercurials.) Although mercury was not volatilized from p-hydroxymercuribenzoate or fluorescein mercuric acetate, the plasmid-bearing strains were resistant to these organomercurials. The ability to volatilize mercury from Hg(2+) and phenylmercury was inducible. The range of inducers included Hg(2+), phenylmercury, and several organomercurials that were not substrates for the degradation system. Mercury-sensitive mutants have been isolated from the parental plasmids pI258 and pII147. Thirty-one such mercury-sensitive strains fall into three classes: (i) mercury-sensitive strains totally devoid of the phenylmercury hydrolase and Hg(2+) reductase activities; (ii) mutants with normal hydrolase levels and no detectable reductase; and (iii) mutants with essentially normal hydrolase levels and low and variable (5 to 25%) levels of reductase activities. The mercury-sensitive strains were also sensitive to phenylmercury, including those with the potential for hydrolase activity.

Drug Resistance, Microbial↗
PubMed1976

Polypeptides of mumps virus.

Mumps virus was propagated in the extra-embryonic fluids of embryonated chicken eggs and was labeled by cionjection of radioactively labeled amino acids. The virus was purified by density gradient centrifugation, and its polypeptides were analyzed by polyarylamide gel electrophoresis. The virus was found to be composed of six polypeptides, ranging in size from 40,000 to 64,000 daltons. Viral proteins 1 and 3 were the glycoproteins of the virons. When the virus particle was treated with noniontic detergents, a small fraction of these glycoproteins could be released into the supernatant. After treatment with nonionic detergents in high salt and alkaline conditions, more of the surface glycoproteins were removed. This treatment also released the smallest viral polypeptide from the virion. The glycoproteins were separated using an affinity chromatographic column of agarose-fetuin. The heavier glycoprotein, viral protein 1, was found to contain both the neuraminidase and hemagglutinating activity. The two glycoproteins were tested for their ability to react in complement-fixing tests with mumps antisera. Only the heavier glycoprotein reacted with antisera possessing both anti-S and anti-V activity. Neither glycoprotein reacted with antisera specific for the S antigen. Thus, it was concluded that this glycoprotein corresponds to the classical V antigen of mumps virus.

Animals↗
PubMed1975

Facilitated transport of calcium by cells and subcellular membranes of Bacillus subtilis and Escherichia coli.

The level of calcium in growing cells is lower than that in the growth medium. Non-energy-dependent uptake of 45-Ca by log-phase cells of Bacillus subtilis occurs under two conditions: at 0 C or in the presence of m-chlorophenyl carbonylcyanide hydrazone. Similar uptake, but quantitatively less, occurs with Escherichia coli cells under the same conditions. Membrane vesicles prepared from B. subtilis or E. coli accumulate 45-Ca by a process that does not depend on added energy sources and is not inhibited by the respiratory poison cyanide. The properties of calcium transport in all cases is consistent with carrier-mediated, facilitated transport with specificity Ca-2+ greater than Sr-2+ greater than Mn-2+ greater than Mg-2+. Upon transfer of cells from 0 C to 20 C, pre-accumulated 45-Ca is released. Heat-killed cells do not accumulate 45-Ca and calcium is released by cells upon addition of toluene (under conditions that do not cause visible lysis). These results suggest that the facilitated uptake of calcium may be utilizing a transport system that normally is responsible for the energy-dependent excretion of calcium from the cells.

Ascorbic Acid↗
PubMed1975

Progress in hepatitis research.

A brief account of recent developments and current nomenclature regarding the viral agents of hepatitis A and B is presented.

Animals↗
PubMed1974

Magnesium transport in Bacillus subtilis W23 during growth and sporulation.

The active transport of magnesium by cells of Bacillus subtilis strain W23 occurs by a highly specific transport system (Mg(2+) is favored over Mn(2+), Co(2+), or Ca(2+)) that is energy dependent (i.e., glucose is required in minimal medium and the system is inhibited by cyanide and m-chlorophenyl carbonylcyanidehydrazone). The rate of magnesium uptake by log-phase B. subtilis cells follows saturation kinetics with a K(m) of 2.5 x 10(-4) M and a V(max) of 4.4 mumol per min per g (dry weight) at 30 C. Manganese is a competitive inhibitor showing a K(i) of 5 x 10(-4) M. During sporulation the rate of magnesium transport declines. This decline in rate is specific for the magnesium system as the manganese and calcium transport rates increase. The residual magnesium transport function in sporulating cells shows both an altered K(m) and an altered V(max). The magnesium content of late sporulating cells is also lower than that for log-phase cells.

Bacillus subtilis↗
PubMed1973

Manganese transport in Bacillus subtilis W23 during growth and sporulation.

Manganese is accumulated in Bacillus subtilis by a highly specific active transport system. This trace element "pump" is insensitive to added magnesium or calcium and preferentially accumulates manganese in the presence of cobalt, iron, and copper. Manganese uptake in B. subtilis is inhibited by cyanide, azide, pentachlorophenol, and m-chlorophenyl carbonylcyanide hydrazone. The uptake of manganese follows Michaelis-Menten kinetics, and the net accumulation of manganese is regulated by increasing the V(max) after exposure to manganese-starvation conditions and by decreasing the V(max) for manganese uptake during growth in excess manganese. The K(m) remains constant during these regulatory changes in V(max). Manganese accumulated during growth is exchangeable for exogenous manganese and can be released from the cells by toluene (which causes leakage but not lysis) or by lysis with lysozyme. Two stages can be distinguished with regard to intracellular manganese during the process of growth and sporulation. During logarithmic growth, B. subtilis maintains a relatively constant internal manganese content, which is a function of the external manganese concentration following approximately a Langmuir adsorption isotherm. At the end of log phase, net accumulation of manganese slows. A second phase of net manganese accumulation begins at about the same time during sporulation as the accumulation of calcium begins. The manganese accumulated during growth and early sporulation is exchangeable and therefore relatively "free"; intracellular manganese is converted later during sporulation into a bound form that cannot be released by toluene or lysozyme.

Azides↗
PubMed1973

Regulation of manganese accumulation and exchange in Bacillus subtilis W23.

An overnight culture of Bacillus subtilis W23 in low-manganese tryptone broth is unable to sporulate and becomes hyperactive with regard to the manganese active transport system during stationary phase. When manganese is added to cells in spent or fresh medium, the cells immediately accumulate a high proportion of the manganese available in the medium. When the hyperactive cells are diluted into broth containing 10 muM Mn(2+), high intracellular manganese levels are reached, and inhibition of ribonucleic acid and protein synthesis occurs. This inhibition is relieved when the intracellular manganese concentration declines to the nontoxic levels characteristic of cells growing in 10 muM Mn(2+). The release of the accumulated manganese is achieved by a reduction in the uptake rate for manganese while the efflux rate remains essentially constant. Inhibitors of ribonucleic acid and protein synthesis prevent the reduction of the high rate of manganese uptake and, therefore, high net concentrations of manganese are maintained in the presence of these inhibitors. The hyperactive manganese uptake system is temperature dependent and inhibited by cyanide and m-chlorophenyl carbonylcyanide hydrazone.

Bacillus subtilis↗
PubMed1972

Manganese-resistant mutants of Escherichia coli: physiological and genetic studies.

Manganese is growth inhibitory for Escherichia coli. The manganese concentration required for inhibition is dependent upon the magnesium concentration of the medium. Mutants have been isolated which are partially resistant to manganese inhibition in both liquid and solid media. From conjugation experiments, the genetic locus for manganese-resistance, mng, appears to be between 34 and 37 min on the E. coli genetic map. Experiments with radioactive (28)Mg lead to the tentative conclusion that the mng mutants are altered in the inhibition constant for manganese as a competitive inhibitor for the mangnesium accumulation system. Once high manganese enters the cells, it displaces internal magnesium and leads to a net cellular loss and hence growth inhibition. The mng mutants are somewhat less subject to manganese-induced magnesium loss under comparable conditions than are manganese-sensitive wild-type cells.

Biological Transport↗
PubMed1972

Mercury resistance in a plasmid-bearing strain of Escherichia coli.

A strain of Escherichia coli carrying genes determining mercury resistance on a naturally occurring resistance transfer factor (RTF) converts 95% of 10(-5)m Hg(2+) (chloride) to metallic mercury at a rate of 4 to 5 nmoles of Hg(2+) per min per 10(8) cells. The metallic mercury is rapidly eliminated from the culture medium as mercury vapor. The volatilizing activity has a temperature dependence and heat sensitivity characteristic of enzymatic catalysis and is inducible by mercuric chloride. Ag(+) and Au(3+) are markedly inhibitory of mercury volatilization.

Catalysis↗