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B Chance

Publications and source records attributed to B Chance.

At least 577 records · Page 32Linked to original sources
PubMed1971

Kinetics and mechanisms of catalase in peroxisomes of the mitochondrial fraction.

1. The primary intermediate of catalase and hydrogen peroxide was identified and investigated in peroxisome-rich mitochondrial fractions of rat liver. On the basis of kinetic constants determined in vitro, it is possible to calculate with reasonable precision the molecular statistics of catalase action in the peroxisomes. 2. The endogenous hydrogen peroxide generation is adequate to sustain a concentration of the catalase intermediate (p(m)/e) of 60-70% of the hydrogen peroxide saturation value. Total amount of catalase corresponds to 0.12-0.15nmol of haem iron/mg of protein. In State 1 the rate of hydrogen peroxide generation corresponds to 0.9nmol/min per mg of protein or 5% of the mitochondrial respiratory rate in State 4. 3. Partial saturation of the catalase intermediate with hydrogen peroxide (p(m)/e) in the mitochondrial fraction suggests its significant peroxidatic activity towards its endogenous hydrogen donor. A variation of this value (p(m)/e) from 0.3 in State 4 to 0 under anaerobic conditions is observed. 4. For a particular preparation the hydrogen peroxide generation rate in the substrate-supplemented State 4 corresponds to 0.17s(-1) (eqn. 6), the hydrogen peroxide concentration to 2.5nm and the hydrogen-donor concentration (in terms of ethanol) to 0.12mm. The reaction is 70% peroxidatic and 30% catalatic. 5. A co-ordinated production of both oxidizing and reducing substrates for catalase in the mitochondrial fraction is suggested by a 2.2-fold increase of hydrogen peroxide generation and a threefold increase in hydrogen-donor generation in the State 1 to State 4 transition. 6. Additional hydrogen peroxide generation provided by the urate oxidase system of peroxisomes (8-12nmol of uric acid oxidized/min per mg of protein) permits saturation of the catalase with hydrogen peroxide to haem occupancy of 40% compared with values of 36% for a purified rat liver catalase ofk(1)=1.7x10(7)m(-1).s(-1) and k'(4)=2.6x10(7)m(-1). s(-1)(Chance, Greenstein & Roughton, 1952). 7. The turnover of the catalase ethyl hydrogen peroxide intermediate (k'(3)) in the peroxisomes is initially very rapid since endogenous hydrogen peroxide acts as a hydrogen donor. k'(3) decreases fivefold in the uncoupled state of the mitochondria.

Animals↗
PubMed1971

Structural measurements in hemoprotiens: use of spin-labeled protoheme as a probe of heme environment.

With the aid of two kinds of spin-labeled protohemins, the nature of the heme-protein interaction of various hemoproteins was investigated. Di- and mono-spin-labeled protohemins were prepared from protohemin and 2,2,5,5-tetramethyl-3-aminopyrrolidine-1-oxyl. The spin-labeled hemins were recombined with apoproteins of hemoglobin (Hb), myoglobin (Mb), cytochrome c peroxidase (EC 1.11.1.5) and horseradish peroxidase (EC 1.11.1.7). Electron paramagnetic resonance spectra of the di- and mono-spin-labeled hemoglobin in 0.1 M potassium phosphate buffer, pH 7.0, at 20 degrees C exhibited moderate immobilization of the labels, while that of cytochrome c peroxidase showed stronger immobilization. Di-spin-labeled horseradish peroxidase showed an EPR spectrum of a simple broad line with peak-to-peak line width of 35 G. This broadening is due to spin-spin interaction between the two labels attached at the 6- and 7-positions of the porphyrin ring. Ligand binding to the spin-labeled hemoproteins altered the EPR line shapes and amplitudes. The former is attributed to the changes in the mobility of the labels and the latter to the magnetic dipolar interaction between the heme iron and free radical. From the strength of this interaction the distance between the iron and the nitroxide radical may be calculated. In the hemoproteins examined, the distances are: Hb 12.5 A, Mb 12.0 A, cytochrome peroxidase approximately 14 A, and horseradish peroxidase 9.0 A.

Chromatography↗