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S B Brown

Publications and source records attributed to S B Brown.

150 records · Page 9Linked to original sources
PubMed1970

Catalatic activity of iron(3)-centred catalysts. Role of dimerization in the catalytic action of ferrihaems.

1. The specific stoicheiometric catalatic activity of deuteroferrihaem is 10-100-fold greater than that for protoferrihaem, depending on pH. It is suggested that the difference in activity may be related to quantitative differences in the extent of dimerization in aqueous solutions of proto- and deutero-ferrihaem (Brown, Dean & Jones, 1970b). 2. A quantitative comparison of the kinetic and equilibrium data implies that the catalytic activities of ferrihaems are determined by the proportion of monomer present. The specific activity of ferrihaem monomer calculated varies inversely with H(+) ion concentration and attains a value equal to the maximal activity of catalase at pH>pK(a)(H(2)O(2)). 3. A comparison of catalatic behaviour in the series of iron(III)-centred catalysts aqua-iron(III) ion, ferrihaem monomer and catalase suggests that the unique feature of catalase action resides in the pH-independence of the reaction.

Catalase↗
PubMed1969

Solution structures of ferrihaem in some dipolar aprotic solvents and their binary aqueous mixtures.

1. Conductivity and u.v. and visible spectroscopic techniques were used to investigate the solution structure of the prosthetic group of the ferric haemoproteins (ferrihaem) in dimethyl sulphoxide, NN-dimethylacetamide, NN-dimethylformamide and sulpholane, and certain of their aqueous mixtures. 2. In neutral or acid dimethyl sulphoxide, chlorohaemin is monomeric and completely dissociated into Cl(-)ion and a ferrihaem species with dimethyl sulphoxide molecules in the fifth and sixth co-ordination positions on iron. 3. In neutral NN-dimethylacetamide and NN-dimethylformamide chlorohaemin is monomeric but is largely undissociated, giving different spectra from that of chlorohaemin in dimethyl sulphoxide. On acidification, dissociation occurs and the dimethyl sulphoxide type of spectrum results. 4. Studies in a fourth solvent, sulpholane, indicate that solvent co-ordinating power (ligand strength) rather than bulk dielectric constant is responsible for dissociation of chlorohaemin. 5. In neutral dimethyl sulphoxide-water mixtures chlorohaemin remains monomeric and completely dissociated, and spectra are independent of mixture composition, except at high water concentrations, when precipitation occurs. In alkaline dimethyl sulphoxide-water mixtures, where the complete solvent mixture range is accessible, ferrihaem is polymeric (probably dimeric) and spectra are dependent on solvent composition. A quantitative analysis indicates that the spectral changes are due to replacement by water of one molecule of co-ordinated dimethyl sulphoxide per ferrihaem aggregate, and do not involve a two-molecule replacement as has been suggested for the alkaline pyridine-water system.

Acids↗
PubMedDate not supplied

Photodynamic therapy using 5-aminolaevulinic acid for oesophageal adenocarcinoma associated with Barrett's metaplasia.

Photodynamic therapy (PDT) is a novel technique for local endoscopic treatment of gastrointestinal neoplasia. Current photosensitisers for PDT may cause prolonged skin phototoxicity. 5-Aminolaevulinic acid (ALA), a precursor of the photosensitiser protoporphyrin IX (PpIX), is more acceptable because of its short half-life and preferential accumulation in mucosa and mucosal tumour. We have treated 12 patients, median age 73 years (range 55-88) with oesophageal adenocarcinoma arising from Barrett's metaplasia (two carcinomas-in-situ, grade 0; 10 carcinomas, grade 1-11A based on endoluminal ultrasound in two and CT scanning in 10 patients). ALA (60 and 75 mg/kg body weight) was given orally in two or five equally divided doses. The PpIX distribution in stomach, normal oesophagus, Barrett's mucosa and carcinoma was measured by quantitative fluorescence photometry. PDT was performed using laser light (630 nm) delivered via a cylindrical diffuser 4-6 h after the first dose of ALA. The patients received one to four sessions of PDT. PpIX accumulation in the mucosa was two to three times that in the lamina propria. The differential distribution between carcinomatous and normal oesophageal mucosa was less marked (carcinoma:normal mucosa ratio = 1.4). Higher doses of ALA increased PpIX accumulation in all tissues but did not increase the differential PpIX distribution between tumour and normal oesophageal mucosa. After PDT using ALA (ALA/PDT), all mucosa showed superficial white necrotic changes and the histology confirmed fibrinoid necrosis. One patient with carcinoma-in-situ had the tumour eradicated after one treatment with no recurrence at 28 months. Another patient with a small T1 tumour required four ALA/PDT treatments, and died of other disease after 36 months. There was no evidence of recurrence. The tumour bulk in the other carcinomas was not significantly reduced. ALA/PDT has a potential for the eradication of small tumours but careful patient selection with endoluminal ultrasound is needed when using ALA/PDT to treat oesophageal cancer.

Adenocarcinoma↗