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Biomedical subjects

D B Knaff

Publications and source records attributed to D B Knaff.

At least 91 records · Page 5Linked to original sources
PubMed1984

Resonance Raman characterization of a novel, oxygen-binding heme protein from Chromatium vinosum.

Resonance Raman spectroscopy was employed to characterize the local heme environment of a high-spin, ligand-binding heme protein from Chromatium vinosum (Chromatium high-spin hemoprotein). High-frequency spectra obtained with both B- and Q-band excitation were found to resemble qualitatively those of deoxyhemoglobin (HbA). Differences between HbA and Chromatium high-spin hemoprotein spectra can be assigned to either the effects of a covalent linkage of the heme vinyls to the protein matrix or alterations in the heme-proximal ligand bonding interaction. Both kinematic and electronic effects were evident. The behavior of heme core-size sensitive modes and low-frequency modes in Chromatium high-spin hemoprotein may be an indication of distortions in the heme geometry of Chromatium high-spin hemoprotein relative to HbA. The effects of covalent bonding of the heme peripheral vinyls upon the vibrational, electronic, and geometric characteristics of the heme active site in Chromatium high-spin hemoprotein are discussed.

Chromatium↗
PubMed1983

Partial purification and characterization of two soluble c-type cytochromes from Chromatium vinosum.

Two c-type cytochromes from Chromatium vinosum have been partially purified and characterized. Cytochrome c550, which appears to function as an electron carrier in the cyclic electron transport chain of this photosynthetic purple sulfur bacterium, has a molecular weight of approximately 15,000 and an oxidation-reduction midpoint potential (Em) of +240 mV at pH 7.4. It has (in the reduced form) an alpha band at 550 nm and a beta band at 520 nm. Cytochrome c551 is characterized by absorbance maxima at 354 and 409 nm in the oxidized form and 418, 523, and 551 nm in the reduced form. The reduced cytochrome reacts with CO. Cytochrome c551 is a monomeric protein with a molecular weight of 18,800 +/- 700 and Em = -299 +/- 5 mV (pH independent between pH 6.3 and 8.0). It appears to lack a methionine axial ligand as indicated by the absence of an absorbance band at 695 nm in the oxidized form.

Chemical Phenomena↗
PubMed1983

L-aspartate transport in the photosynthetic bacterium Chromatium vinosum.

The photosynthetic purple sulfur bacterium Chromatium vinosum appears to contain two active transport systems for L-aspartate. The higher affinity system (S0.5 = 60 microM) appears to be an electrogenic aspartate/H+ symport and the lower affinity system (S0.5 = 220 microM) appears to involve an aspartate/Na+ symport. In addition to a possible role in providing the driving force for aspartate uptake, transmembrane Na+ gradients may also have allosteric effects on aspartate transport in C. vinosum.

Aspartic Acid↗
PubMed1983

Reduction of laccase type 1 copper by 3,4-dihydroxyphenylalanine and other catechol derivatives.

3,4-Dihydroxyphenylalanine (DOPA) is not a preferred substrate of Rhus vernicifera laccase, as rate constants for the anaerobic reduction of the type 1 cupric atom by L-DOPA (6.3 X 10(1) M-1 s-1), D-DOPA (2.6 X 10(1) M-1 s-1), and L-DOPA methyl ester (2.6 X 10(1) M-1 s-1) are considerably smaller than k1 (catechol) (7 X 10(2) M-1 s-1) and rate constants characteristic of numerous other nonphysiological organic substrates (25 degrees C, pH 7.0, I = 0.5 M). The reactions of DOPA derivatives with laccase are unique, however, in that a two-term rate law pertains: kobsd = k0 + k1[phenol]; k0(L-DOPA) = 7 X 10(-2) s-1. The reactivities of other catechol derivatives (pyrogallol, gallic acid, and methyl gallate) with laccase type 1 copper were also examined.

Catechols↗
PubMed1981

Spectroscopic studies of stellacyanin derivatives.

Two covalently modified derivatives of the apoprotein of the blue copper protein stellacyanin have been prepared. In one case, a dansyl group was linked to the cysteine at the copper binding site of apostellacyanin; in the other, a nitrophenol moiety has been attached to this same cysteine. Fluorescence yields and emission maxima of the dansylated protein and pK determinations of the nitrophenol group linked to the protein suggest that the solvent microenvironment at the copper binding site of apostellacyanin is quite similar to bulk water.

Binding Sites↗
PubMed1981

Reactivity of cuprous stellacyanin as a quinone and semiquinone reductase.

The reactivity of cuprous stellacyanin as a quinone and semiquinone reductase has been examined. Rate constants (25.0 degrees C) measured for the oxidation of stellacyanin by 1,4-benzoquinone and benzosemiquinone are 2.3 X 10(4) M-1 s-1 (delta H not equal to = 4.4 kcal/mol, delta S not equal to = -24 eu) and 5.1 X 10(6) M-1 s-1, respectively [pH 7.0, I = 0.1 M (phosphate)]. The agreement of these rate constants with those calculated on the basis of relative Marcus theory is discussed. Stellacyanin is more effective than laccase in quenching benzosemiquinone, suggesting that the physiological role of this metalloprotein is to regulate the concentration of free radicals generated through the laccase-catalyzed oxidation of phenols.

Calorimetry↗
PubMed1981

Electrochemical titrations of a ferredoxin-ferredoxin:NADP+ oxidoreductase complex.

Potentiometric titrations employing an electrochemical thin-layer cell indicate that complex formation between ferredoxin and ferredoxin:NADP+ oxidoreductase alters the midpoint oxidation-reduction potentials of both proteins. The midpoint potential of ferredoxin the complex becomes 22 +/- 6 mV more negative compared to ferredoxin alone while the midpoint potential of ferredoxin:NADP+ oxidoreductase becomes 23 +/- 4 mV more positive on complex formation.

Ferredoxin-NADP Reductase↗