Thomas C. Hollocher
Brandeis University
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Archives of Biochemistry and Biophysics | 1984
Thomas C. Hollocher
15N, 18O Tracer studies were applied to the aerobic oxidation of nitrite to nitrate by the chemolithotrophic bacterium, Nitrobacter agilis. It was established that, in conversion of nitrite to nitrate, one oxygen atom of nitrate arose from water and none from O2 or inorganic phosphate. This result confirms that of Kumar et al. [(1983) FEBS Lett. 152, 71-74]. Oxygen exchange between water and inorganic phosphate was small and that between water and nitrite or nitrate or any reaction intermediates between these two was not detected. Oxidation of nitrite was, therefore, effectively irreversible under the conditions employed. The uptake of extracellular phosphate was sufficient to allow significant transfer of 18O from phosphate to nitrate if oxidative phosphorylation had occurred by way of a P-O-N anhydride between phosphate (or ADP) and nitrate. The results are, therefore, inconsistent with the occurrence of a reaction of this type during nitrite oxidation.
Biochemical and Biophysical Research Communications | 1988
Xiao-bing Ji; Thomas C. Hollocher
Seven bacteria representing seven genera of enteric bacteria, in addition to Escherichia coli, were shown to reduce nitrite to NO under anaerobic conditions when the cells were grown as nitrate respirers. NO production was inhibited by nitrate and azide and was self limiting, just as was found to be the case previously with E. coli and its nitrate reductase. Maximum initial rates of NO production were observed at pH 5.5-6.
Science | 1972
Edwin E. Huling; Thomas C. Hollocher
The average steady-state contamination of groundwater by road salt in the suburban area around Boston, on the assumption that current rates of application of salt will continue, is about 160 milligrams of sodium chloride per liter of water (100 milligrams of chloride per liter). This value is compared with values of 50 to 100 milligrams of chloride per liter found rather commonly now in town wells in eastern Massachusetts. These salt concentrations may be of concern to persons on low-sodium diets and to persons who obtain water from wells in the vicinity of major highways where salt concentrations could be several times higher than average.
PALAIOS | 2001
Thomas C. Hollocher; Karen Chin; Kurt Hollocher; Michael A. Kruge
Abstract The Cretaceous Two Medicine Formation of northwestern Montana has yielded blocky, calcareous coprolites that contain abundant fragments of conifer wood and were produced by large herbivorous dinosaurs. The coprolites are generally dark gray to black in color due to a dark substance confined chiefly within what originally were the capillaries of tracheid and ray cells of xylem. This substance is a kerogen that consists in part of thin-walled vesicles 0.1–1.3 μm in diameter. Pyrolysis products of this kerogen are diagnostic of a bacterial origin with a possible contribution from terrestrial plants. The vesicular component is interpreted as the residue of bacterial cells, whereas a second filamentous component, closely associated with the vesicles, may be the residue of an extracellular binding material, such as glycocalyx. At least two episodes of calcification of the coprolite are recognized by manganous cathodoluminescence. The earlier of these infilled the capillary channels of the conifer fragments. Wood cell walls, voids, cracks, and small burrows were filled during the later episode. Microprobe data confirm these results and show that phosphate is sequestered in the capillaries. These observations suggest that bacteria within the capillaries induced initial mineralization of the coprolite, and, in so doing, created barriers that protected organic residues from subsequent destruction. Early onset of mineralization is consistent with the degree of preservation of woody xylem found in the coprolites.
Biochemical and Biophysical Research Communications | 1992
Tom Turk; Thomas C. Hollocher
The stoichiometric relationship between thiol oxidized and NO reduced was studied for the reaction catalyzed by nitric oxide reductase from Paracoccus denitrificans. The reaction systems consisted of dithiothreitol, ascorbate, phenazine methosulfate, enzyme and NO, or that system minus ascorbate. The mole ratio of thiol groups oxidized to NO reduced was observed to be 2.3 to 1.5 over a range of NO from 0.09 to 0.35 mumol. A ratio of 1.0 was expected for the simple reduction of NO by 1-electron to N2O. The oxidation of additional thiol is attributed to the trapping of nitrosyl hydride (nitroxyl, NO/NOH) by thiol.
Biochimica et Biophysica Acta | 1971
Barbara M. Sanborn; Norman T. Felberg; Thomas C. Hollocher
Abstract 1. 1. Bromopyruvate has been found to be a potent irreversible inhibitor of succinate dehydrogenase (succinate:(acceptor) oxidoreducatase, EC 1.3.99.1). While the kinetics of inactivation show a saturation effect, they do not fit the simple model for an active-site-directed irreversible inhibitor. Instead, a concentration dependent plateau is observed. A similar phenomenon occurs when N- ethylmaleimide is the alkylating agent. Reversible inhibitors and substrates protect succinate dehydrogenase from activation by bromopyruvate and N- ethylmaleimide . Both reagents have similar relative reactivities toward the enzyme and 2-nitro-5-thiolbenzoic acid dianion. 2. 2. The absorption and dithionite bleaching spectra are not greatly affected by the reaction of enzyme with bromopyruvate, but the ability of succinate to bleach is lost. A decrease in hydrogen exchange capacity parallels the decrease in assay activity.
PALAIOS | 2010
Kurt Hollocher; Thomas C. Hollocher; J. Keith Rigby
Abstract A single, low-density (1.58 g/cm3), phosphatic coprolite recovered from a fluvial Triceratops site in the Upper Cretaceous Hell Creek Formation of eastern Montana contains small quantities of minute bone or tooth fragments, kerogenized plant residues (pollen, spores, sporangia, and cuticle), hyphae of probable fungal origin, and small detrital mineral grains in a fine-grained, highly porous matrix. Roughly 30% of the matrix, composed almost entirely of microcrystalline francolite (carbonate-fluorapatite), is composed of thin-walled vesicles of roughly spherical shape, 0.5–3 µm in diameter. These vesicles are interpreted as mineral pseudomorphs of organic particles, probably including fecal bacteria, existing in the original scat. This structurally well-preserved coprolite is likely derived from the scat of a bone-digesting carnivorous animal, contains much or all of the autochthonous apatite of the original scat, and lacks permineralization that commonly produces a densely lithified object of low porosity. This is the first detailed description of a coprolite of this type from Mesozoic fluvial deposits. This evidence supports the view that dietary calcium phosphate could precipitate rapidly in the scat of ancient carnivorous animals, providing the structural strength to allow preservation of internal organic forms in great detail.
Biochimica et Biophysica Acta | 1993
Alison M. Jones; Thomas C. Hollocher
Abstract Nitric oxide reductase from Achromobacter cycloclastes was solubilized with dodecyl maltoside from membranes and substantially purified by hydroxyapatite column chromatography. Preparations of enzyme had purities estimated to be 65–72% and specific activities of about 3 μmol NO/min per mg protein when measured at 30°C and pH 5.5 using ascorbate/phenazine methosulfate as the reducing system. Preparations lacked nitrite reductase activity. The enzyme consists of two peptides of approx. 38 and 17.5 kDa, and is identified as a cytochrome bc complex for which the mol ratio of cytochrome c to cytochrome b is about 1:1. A heme c containing band of approx. 55 kDa would appear to be a 1:1 complex or compound of the 38 and 17.5 kDa peptides. These and other observations suggest that A. cycloclastes possesses a nitric oxide reductase similar to that previously purified from Pseudomonas stutzeri and Paracoccus denitrificans . In contrast to the cytochrome cd 1 -type nitrite reductase of the latter two bacteria, the nitrite reductase of A. cycloclastes is a copper protein. This is the first reported characterization of nitric oxide reductase from a denitrifier with a Cu-containing nitrite reductase, and provides further evidence that the denitrification pathway in such bacteria requires nitric oxide reductase and proceeds by way of NO as an intermediate.
Biochemical and Biophysical Research Communications | 1982
Eric A.E. Garber; Domenic Castignetti; Thomas C. Hollocher
Summary Minimum →H + /2e − ratios for both the NO→1/2N 2 O and NO→1/2N 2 reactions were about 3.7 with denitrifying Paracoccus denitrificans . These ratios are only slightly less than those obtained with other N-oxides similarly linked to the oxidation of endogenous substrate. Active transport of [ 14 C]L-proline was supported by the above two reactions of NO in denitrifying cells. NO failed to promote proline uptake with aerobically grown cells. The uncoupler, carbonyl cyanide m -chlorophenylhydrazone, abolished proline uptake and greatly diminished proton translocation with NO and other N-oxides. The results directly demonstrate for the first time that reduction of exogenous NO is energy yielding in a denitrifying bacterium.
Current Microbiology | 1981
Jakob K. Kristjansson; Thomas C. Hollocher
We report the first partial purification of nitrous oxide reductase, a unique and labile enzyme of denitrifying bacteria. The procedure, which required anaerobic conditions throughout, resulted in a 60-fold purification relative to crude lysate in the case ofParococcus denitrificans. The molecular weight was estimated by gel exclusion chromatography to be about 85,000. The partially purified enzyme is inactivated rapidly by O2, dithionite, and mercaptoethanol and is reversibly inhibited by moderate concentrations of common salts. Up to 80% of the original activity can be reconstituted following O2 inactivation by incubating the enzyme with reduced benzyl viologen for 2 to 3 h. TheVmax pH profile shows a broad maximum at pH 8. The enzyme is irreversibly retained by common anion exchangers in the range pH 7 to 8 but can be eluted in acceptable yield as one of the last components from an imidazole-based anion exchange material by means of a pH gradient. This behavior implies that nitrous oxide reductase is very acidic. Among the several peptides observed by sodium dodecyl sulfate slab electrophoresis, only two, with apparent molecular weights of 58,000 and 25,000, correlated closely with the activity of fractions eluted from the imidazole column. These two peptides together comprised about 30% of the total protein in the fractions with highest specific activity.