Respiratory enzymes of Thiobacillus ferrooxidans. A kinetic study of electron transfer between iron and rusticyanin in sulfate media

Thiobacillus ferrooxidans is a chemolithotrophic bacterium capable of fulfilling all of its energy requirements from the oxidation of soluble ferrous sulfate. Rusticyanin is a soluble blue copper protein found in abundance in the periplasmic space of this bacterium. The one-electron transfer reaction between soluble iron and purified rusticyanin has been studied by stopped flow spectrophotometry in acidic solutions containing sulfate. Second order rate constants for the reduction of rusticyanin by Fe2+, FeHSO4+, and FeSO4(0) were 0.022, 0.73, and 2.30 M-1 s-1, respectively. The pseudo-first order rate constant for the reduction of rusticyanin exhibited substrate saturation when the concentration of the total ferrous ion was varied in solutions of limiting sulfate. This saturation behavior was quantitatively described using the values of the second order rate constants listed above and the distribution of the total ferrous ion into its water-, bisulfate-, and sulfate-coordinated forms. Second order rate constants for the oxidation of rusticyanin by Fe3+ and FeSO4+ were 0.73 and 0.26 M-1 s-1, respectively. The electron transfer reactions between iron and rusticyanin monitored in vitro were far too slow to support the hypothesis that rusticyanin is the primary oxidant of ferrous ions in the iron-dependent respiratory electron transport chain of T. ferrooxidans.     

Selection of sites for egg deposition and spawning dynamics in the waccamaw darter

Synopsis We provided 93 experimental spawning covers for the waccamaw darter. We grouped the covers (3 sizes of slate and one of concave tile) in three arrangements at six Lake Waccamaw locations to separate the variables of water depth, distance from shore, cover density and cover type. Tag returns of marked males suggest low fidelity for nest sites. Egg production under the 3 different sizes of slate was not significantly different. Egg production under the tile was significantly less than that under the slates. Egg production was significantly higher off the undeveloped southeastern shore in 2 m of water and lowest at the shallowest location with the highest experimental cover density. The number of eggs in nest is positively correlated with male size. We conclude that medium size slate covers placed in a linear arrangement in 2 m of water on a mixed sand bottom result in the highest egg production for the waccamaw darter.     

A resolution of the ascertainment sampling problem I. Theory

We consider the "ascertainment problem" arising when families are sampled by a nonrandom sampling process and, for the purpose of estimating genetic parameters, some assumption must be made about the process by which families enter the sample. A resolution of this problem, involving conditioning the likelihood of the sample on that part of the data relevant to ascertainment, is put forward. Numerical examples illustrating the properties of the procedure are provided.     

Effect of divers anions on the electron-transfer reaction between iron and rusticyanin from Thiobacillus ferrooxidans

Rusticyanin is a soluble blue copper protein found in abundance in the periplasmic space of Thiobacillus ferrooxidans, an acidophilic bacterium capable of growing chemolithotrophically on soluble ferrous sulfate. The one-electron-transfer reactions between soluble iron and purified rusticyanin were studied by stopped-flow spectrophotometry in acidic solutions containing each of 14 different anions. The second-order rate constants for both the Fe(II)-dependent reduction and the Fe(III)-dependent oxidation of the rusticyanin varied as a function of the identity of the principal anion in solution. Analogous electron-transfer reactions between soluble iron and bis(dipicolinato)cobaltate(III) or bis(dipicolinato)ferrate(II) were studied by stopped-flow spectrophotometry under solution conditions identical with those of the rusticyanin experiments. Similar anion-dependent reactivity patterns were obtained with soluble iron whether the other reaction partner was rusticyanin or either of the two organometallic complexes. The Marcus theory of outer-sphere electron transfer reactions was applied to this set of kinetic data to demonstrate that the rusticyanin may possess at least two electron-transfer pathways for liganded iron, one where the pattern of electron-transfer reactivity is controlled largely by protein-independent activation parameters and one where the protein exhibits an anion-dependent kinetic specificity. The exact role of rusticyanin in the iron-dependent respiratory electron transport chain of T. ferrooxidans remains unclear.