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M J Todd

Publications and source records attributed to M J Todd.

68 records · Page 4Linked to original sources
PubMed1987

Purification and characterization of the nickel-containing multicomponent urease from Klebsiella aerogenes.

Klebsiella aerogenes urease was purified 1,070-fold with a 25% yield by a simple procedure involving DEAE-Sepharose, phenyl-Sepharose, Mono Q, and Superose 6 chromatographies. The enzyme preparation was comprised of three polypeptides with estimated Mr = 72,000, 11,000, and 9,000 in a alpha 2 beta 4 gamma 4 quaternary structure. The three components remained associated during native gel electrophoresis, Mono Q chromatography, and Superose 6 chromatography despite the presence of thiols, glycols, detergents, and varied buffer conditions. The apparent compositional complexity of K. aerogenes urease contrasts with the simple well-characterized homohexameric structure for jack bean urease (Dixon, N. E., Hinds, J. A., Fihelly, A. K., Gazzola, C., Winzor, D. J., Blakeley, R. L., and Zerner, B. (1980) Can. J. Biochem. 58, 1323-1334); however, heteromeric subunit compositions were also observed for the enzymes from Proteus mirabilis, Sporosarcina ureae, and Selemonomas ruminantium. K. aerogenes urease exhibited a Km for urea of 2.8 +/- 0.6 mM and a Vmax of 2,800 +/- 200 mumol of urea min-1 mg-1 at 37 degrees C in 25 mM N-2-hydroxyethylpiperazineN'-2-ethanesulfonic acid, 5.0 mM EDTA buffer, pH 7.75. The enzyme activity was stable in 1% sodium dodecyl sulfate, 5% Triton X-100, 1 M KCl, and over a pH range from 5 to 10.5, with maximum activity observed at pH 7.75. Two active site groups were defined by their pKa values of 6.55 and 8.85. The amino acid composition of K. aerogenes urease more closely resembled that for the enzyme from Brevibacter ammoniagenes (Nakano, H., Takenishi, S., and Watanabe, Y. (1984) Agric. Biol. Chem. 48, 1495-1502) than those for plant ureases. Atomic absorption analysis was used to establish the presence of 2.1 +/- 0.3 mol of nickel per mol of 72,000-dalton subunit in K. aerogenes urease.

Amino Acids↗
PubMed1980

The effect of root resection on the sealing property of root canal obturations.

Root canal systems of extracted anterior teeth were obturated with sealer and either multiple gutta-percha cones or single silver cones. The effect of root resection on the sealing property of these obturating materials was evaluated by autoradiographic methods. Results indicate that root resection with a rotary instrument in a high-speed handpiece does not adversely affect the sealing property of well-condensed gutta-percha-sealer obturations.

Apicoectomy↗
PubMed1975

The effects of thermal injury on pulpal hydrolases.

The effects of thermal injury on pulpal protein levels and the activities of selected pulpal hydrolases were determined 48 hours following injury. At this time protein levels were significantly greater while enzyme activities were significantly lower in thermally insulted teeth. The implications of these studies are discussed.

Animals↗