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Biomedical subjects

J Lampe

Publications and source records attributed to J Lampe.

5 recordsLinked to original sources
PubMed1978

The role of cytochrome P-450 in the toxicity of xenobiotics.

The cytochrome P-450 containing mixed-function oxidase system bound to the ergastoplasmic membrane plays an essential role both in the detoxification as well as in the activation of numerous xenobiotics. In many cases, this enzyme system initiates the formation of reactive electrophilic intermediates (epoxides, free radicals, carbenes) which may induce cytotoxic, mutagenic and carcinogenic effects by reacting with various cell constituents. In most cases, the active metabolites are covalently bound to the proteins and nucleic acids, but the binding to lipids or the initiation of the lipid peroxidation is also important. In the activation of xenobiotics by N-hydroxylation or N-dealkylation an aminoxidase is of special importance which is independent of cytochrome P-450. The intermediates arising from this enzyme reaction frequently become biologically active only after being stabilized by an ester bond.

Aflatoxins↗
PubMed1975

Studies on electron transfer between mercury electrode and hemoprotein.

The electrochemical behaviour of ferricytochrome c, metmyoglobin and methemoglobin was studied using d.c., a.c. and differential pulse polarography, and controlled potential electrolysis. 1. The three hemoproteins yield d.c. polarographic steps, and peaks in differential pulse polarograms, the height of which is proportional to concentration. The charge transfer is influenced by strong adsorption. 2. The concentration dependence of the a.c. polarograms indicates structural changes in the adsorbed molecules. 3. The reduction products of controlled potential electrolysis of metmyoglobin and methemoglobin have absorption spectra identical with the native control samples. The affinity for oxygen and the cooperativity in hemoglobin are not affected by the reaction at the electrode. 4. The charge transfer proceeds via adsorbed, already reduced, molecules to freely diffusible proteins.

Binding Sites↗
PubMed1975

[The effect of the immobilization of hemoglobin on its oxygen binding].

Hemoglobin (Hb) covalently fixed to CM-Sephadex was found to bind oxygen in weakly acidic medium with higher affinity than free Hb. The opposite relation is seen in the alkaline pH region. The alkaline Bohr effect was determined to be -0.2 only. Cooperativity is pH dependent. The sigmoid coefficient at pH 6 is 0.7; at pH 8.7 n was determined to be 1.3. As the reason of these altered binding properties a blockade of the primary amino groups, disturbance of the salt bridges, and restrained cooperative mobility of the Hb-subunits are discussed. The Hill coefficient is additionally lowered by the heterogeneity of the immobilized Hb.

Dextrans↗
PubMed1975

[Oxygen binding of hemoglobin following covalent fixation in the deoxy- and oxy- conformation].

Deoxyhemoglobin (deoxyHB) and oxyhemoglobin (HbO2) were covalently fixed to BrCN-activated Sephadex G-200. At pH 6, the oxygen semi-saturation pressure for the deoxyHb coupling product was 14.1, and for the HbO2 coupling product, 7.2 mm Hg. The alkaline Bohr effect delta was calculated to be - 0.55 and - 0.4 respectively. The Hill coefficients n are for both Hb derivatives between 1.4 and 1.5, independently of pH (for free Hb the respective values are pO2 50% = 18.2 mm Hg, delta = -0.55 and n = 2.5). Non-crosslinked dextran and Sephadex G-200 have no influence upon the affinity of free Hb to oxygen and upon cooperativity. As a reason for the varying oxygen-binding properties for the two Hb derivatives it is assumed that the amino group of valin alpha 1 is involved in the HbO2 fixation. In deoxyHb, this group is not probably converted. The reduced Hill coefficients and enhanced oxygen affinity are assumed to be due to impairment of the inter-chain contacts, to restrained cooperative mobility, and heterogeneity of the coupling products.

Adult↗