30 research outputs found
Reductive activation of potential antitumor bis(aziridinyl)benzoquinones by xanthine oxidase: Competition between oxygen reduction and quinone reduction
The reduction of a series of 2,5-bis(1-aziridinyl)-1,4-benzoquinone (BABQ) derivatives with various 3,6 substituents by the enzyme xanthine oxidase has been studied. The reduction rate has been assayed by measuring the rate of reduction of cytochrome c, which is very efficiently reduced by reduced BABQ species. Under nitrogen, the reduction rate correlated with the quinone reduction potential and steric parameters. Comparing reduction rates under nitrogen and air demonstrates that at BABQ concentrations > 25 μm the competition for electrons from xanthine oxidase between oxygen and the BABQ derivative is dominated by the latter. This is also confirmed by the effect of superoxide dismutase (SOD): in the presence of a BABQ derivative, cytochrome c reduction can be totally inhibited by SOD, although the required amount of SOD depends on the redox potential of the quinones. This indicates that SOD causes the equilibrium between semiquinone and superoxide to shift, resulting in a decrease of the semiquinone concentration. It is concluded that reduction by xanthine oxidase is a simple and effective method for reducing aziridinylbenzoquinones
The stimulatory effect of albumin on luteinizing hormone-stimulated Leydig cell steroid production depends on its fatty acid content and correlates with conformational changes
__Abstract__
The effects of purified albumin species and albumin fragments (0.2–1% w/v) on short-term (4 h) steroid secretion by immature rat Leydig cells, in the presence of a maximally stimulating dose of luteinizing hormone (LH), were investigated. Human albumin and the peptic fragment (comprising residues 1–387) enhanced pregnenolone production in isolated rat Leydig cells, whereas chicken albumin and the tryptic fragment (comprising residues 198–585) were not active.
This stimulatory effect of human albumin and the peptic fragment correlated with the potential of these proteins to undergo a pH-dependent neutral-to-base transition as measured by circular dichroism. The tryptic fragment and chicken albumin did not have the potential to undergo such a transition. The pH-dependent conformational changes of albumin and fragments thereof occurred in parallel with a change in the binding affinity for testosterone and pregnenolone.
The fatty acid oleic acid and the drug suramin, only when present in a molar ligand-to-albumin ratio equal to or higher than 2, inhibited the albumin-mediated stimulation of steroid production.
These data show that the stimulatory effects of albumin species on LH-induced Leydig cell pregnenolone production depend on their fatty acid content and correlate with the potential of these molecules to undergo conformational changes. It is unknown via which mechanisms albumin exerts its stimulatory effect, but the LH action through the cyclic AMP pathway seems not to be affected
The Interaction of 2,3-Diphosphoglycerate with Human Hemoglobin: EFFECTS ON THE ALKALINE AND ACID BOHR EFFECT
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143053.pdf (publisher's version ) (Open Access
Some aspects of cooperativity in human hemoglobin
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143046.pdf (publisher's version ) (Open Access
Allosteric models for the interaction of 2,3-diphosphoglyceric acid with hemoglobin
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143085.pdf (publisher's version ) (Open Access
Comparison of the oxygen and proton binding behavior of human hemoglobin A and A2
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143004.pdf (publisher's version ) (Open Access
Titration Behavior of Histidines in Human, Horse, and Bovine Hemoglobins
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143092.pdf (publisher's version ) (Open Access
Hydrogen-Ion-Titration Studies of Pancreatic Phospholipase A and Its Zymogen
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143076.pdf (publisher's version ) (Open Access
Effect of 2,3-diphosphoglycerate on the Bohr effect of human adult hemoglobin
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143106.pdf (publisher's version ) (Open Access
Hydrogen ion titration study of the histidine residues of horse myoglobin
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143075.pdf (publisher's version ) (Open Access