Biomedical subjects

K Pommerening

Publications and source records attributed to K Pommerening.

3 recordsLinked to original sources

PubMed1979

Electrochemical investigations on the oxygen activation by cytochrome P-450.

The application of cytochrome P-450 in substrate conversion is complicated both due to the limited stability and the cofactor regeneration problems. To overcome the disadvantages of NADPH consumption the transfer of the reduction equivalents from an electrode into the cytochrome P-450-system was studied: 1. NADPH was cathodically reduced at a mercury pool electrode. By immobilization of NADP on dialdehyde Sephadex the reductive recycling was possible. 2. Different forms of reduced oxygen were produced by the cathode: a) The reaction of O2- with deoxycorticosterone yields a carboxylic acid derivative. In contrast the cytochrome P-450 catalyzed NADPH-dependent reaction with the same substrate gives corticosterone, O2- represents only an intermediate in the activation of oxygen and is not the "activated oxygen" species. b) Molecular oxygen was reduced to HO2- and H2O2, respectively. The interaction of adsorbed cytochrome P-450 on the electrode surface with the reduced oxygen species in the absence of NADPH was studied. The electrochemically generated peroxide seems to be more active than added H2O2. 3. In a model of electro-enzyme-reactor several substrates were hydroxylated by microsomal cytochrome P-450 with cathodically reduced oxygen which substitutes NADPH.

Animals↗

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↗