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L M Cameron

Publications and source records attributed to L M Cameron.

7 recordsLinked to original sources
PubMed2001

Transient-state reduction and steady-state kinetic studies of menaquinol oxidase from Bacillus subtilis, cytochrome aa3-600 nm. Spectroscopic characterization of the steady-state species.

Cytochrome aa3-600 or menaquinol oxidase, from Bacillus subtilis, is a member of the heme-copper oxidase family. Cytochrome aa3-600 contains cytochrome a, cytochrome a3, and CuB, and each is coordinated via histidine residues to subunit I. Subunit II of cytochrome aa3-600 lacks CuA, which is a common feature of the cytochrome c oxidase family members. Anaerobic reduction of cytochrome aa3-600 by the substrate analogue 2,3-dimethyl-1,4-naphthoquinone (DMN) resolves two distinct kinetic phases by stopped-flow, single-wavelength spectrometry. Global analysis of time-resolved, multiwavelength spectra shows that during these distinct phases cytochromes a and a3 are both reduced. Cyanide binding to cytochrome a3 enhances the fast phase rate, which in the presence of cyanide can be assigned to cytochrome a reduction, whereas cytochrome a3-cyanide reduction is slow. The steady-state activity of cytochrome aa3-600 exhibits saturation kinetics as a function of DMN concentration with a Km of 300 microM and a maximal turnover of 63.5 s(-1). Global kinetic analysis of steady-state spectra reveals a species that is characteristic of a partially reduced oxygen adduct of cytochrome a3-CuB, whereas cytochrome a remains oxidized. Electron paramagnetic resonance (EPR) spectroscopy of the oxidase in the steady state shows the expected signal from ferricytochrome a, and a new EPR signal at g = 2.01. A model of the catalytic cycle for cytochrome aa3-600 proposes initial electron delivery from DMN to cytochrome a, followed by rapid heme to heme electron transfer, and suggests possible origins of the radical signal in the steady-state form of the enzyme.

Anaerobiosis↗
PubMed1998

High throughput purification of combinatorial libraries.

This article summarizes recent advances at MDS Panlabs which provide for the high-throughput preparative HPLC purification of our Optiverse screening library. Topics covered include unique methods for the preparation, purification, characterization, and plating of purified screening compounds. Also discussed are procedures for data tracking as samples proceed through the purification process.

Chemistry, Organic↗
PubMed1998

Investigation of CO binding and release from Mo-nitrogenase during catalytic turnover.

During enzymatic turnover in the presence of CO, Mo-nitrogenase has been shown to generate two different EPR signals termed lo-CO (PCO = 0.08 atm) and hi-CO (PCO = 0.5 atm). When the formation of hi-CO is monitored under the conditions of very low electron flux, a 2 min lag is observed prior to the initial detection of the signal followed by a near-linear rate of formation during which the S = 3/2 cofactor signal exhibits similar decay kinetics. Increasing the electron flux produces a significant increase in the rate of both the formation of hi-CO and the decay of the S = 3/2 cofactor. These results are interpreted in terms of a state of the enzyme (redox or structural) generated only during turnover which is needed to initially bind CO to the cofactor. Under high electron flux conditions, new EPR inflections are observed at g = 5.78, 5.15 and g = 1.95, 1.81 and tentatively assigned to S = 3/2 and 1/2 states of the CO-bound cofactor and 1 equiv of oxidized P cluster, respectively. Sudden removal of CO from the environment results in the slow decay (>10 min) of both the hi-CO signal and CO inhibition of acetylene reduction activity. The use of ethylene glycol to quench enzymatic activity strongly inhibits the decay of hi-CO (in the presence of CO) and the subsequent decay of lo-CO (after removal of CO) but does not prevent the reversible interconversion hi-CO left and right arrow lo-CO + CO.

Adenosine Triphosphate↗
PubMed1989

Use of exfoliated cells to study tissue-specific levels of beta-carotene in humans.

This study was designed to explore the feasibility of using exfoliated cells to study beta-carotene incorporation into different epithelial tissues in humans. Exfoliated cells were collected from the oral cavities (by brushing the oral mucosa) and from the urogenital tracts (by centrifuging urine samples) of 36 females and basal levels of beta-carotene (without oral supplementation) were determined. Beta-carotene levels in cells from the two sites differed significantly, although a weak correlation was observed. As a second aspect of the study, 10 of these females were given oral supplementation with beta-carotene (90 mg twice weekly for 4 weeks). Beta-carotene levels increased significantly in both exfoliated urogenital tract (6.8-fold) and oral mucosa (5-fold) cells. However, the supplemented levels remained significantly different for the two types of cells. Beta-carotene levels did not change in individuals receiving a placebo treatment (n = 7). These studies suggest that exfoliated cells collected from different sites may be of value in quantifying tissue levels of beta-carotene during cancer intervention trials.

Adult↗
PubMed1985

Triazene metabolism. IV. Derivatives of hydroxymethyltriazenes: potential prodrugs for the active metabolites of the anti-tumour triazene, DTIC.

A series of derivatives of the anti-tumour hydroxymethyltriazenes have been investigated for activity in vivo and in vitro. Acetoxymethyltriazenes are active in vivo against the TLX5, P388 and PC6 tumours in mice, and inhibit the growth of TLX5, Np and Li cells in vitro without metabolic activation. The acetoxymethyltriazenes are comparable with the hydroxymethyltriazenes and monomethyltriazenes in their spectrum of activity and thus appear to be prodrugs for these species. On the other hand, a methoxymethyltriazene was found to be active on the TLX5 tumour in vivo, but did not inhibit the growth of Np cells in vitro. This latter observation is consistent with the anticipated chemical stability of the methoxymethyltriazene and the requirement for metabolic O-demethylation to generate an active species. Acetoxymethyltriazenes do not require metabolic intervention and break down chemically in phosphate buffer to the hydroxymethyltriazene, which in turn loses formaldehyde to give the incipient methylating agent, the monomethyltriazene.

Animals↗
PubMed1985

Triazene metabolism. V. Chemical and biological properties of N,N-bis-[(1-aryl-3-methyltriazen-3-yl)-methyl]-methylamines: potential prodrugs for the cytotoxic monomethyltriazenes.

N,N-Bis-[(1-aryl-3-methyltriazen-3-yl)-methyl]-methylamines, 'bistriazenes', have anti-tumour activity against the TLX5 and PC6 mouse tumours and inhibit the growth of tumour cells growing in culture, without metabolic activation. The biological activity of the bistriazene appears to derive from facile hydrolysis to the cytotoxic monomethyltriazene, Ar-N = N-NHMe, and it is suggested that the bistriazene may be a good prodrug from for the 'active' metabolite of the anti-tumour dimethyltriazene, Ar-N-N = N-NME2. A kinetic study of the bistriazene hydrolysis shows that the reaction is retarded by electron-withdrawing substituents in the aryl group. The results can be interpreted by a mechanism in which the bistriazene behaves as an 'animal' (i.e. N-CH2-N) and undergoes anchimerically assisted fragmentation, via an iminium ion intermediate, to the monomethyltriazene.

Animals↗