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Biomedical subjects

F W Dahlquist

Publications and source records attributed to F W Dahlquist.

At least 127 records · Page 7Linked to original sources
PubMed1975

Malate dehydrogenase, anticooperative NADH, and L-malate binding in ternary complexes with Supernatant pig heart enzyme.

Supernatant malate dehydrogenase from pig heart, a dimeric protein containing two very similar or identical subunits, shows negatively cooperative (anticooperative) interactions between NADH binding sites in the presence, but not in the absence, of 0.1 M L-malate. This behavior is observed consitently whether the technique used employs protein fluorescence quenching, NADH fluorescence enhancement, or ultrafiltration dialysis. Fluorescence titration shows that L-malate is also anticooperatively bound in the presence of saturating concentrations of NADH. The data are consistent with an "induced asymmetry" model in which conformational change accompanies the formation of the ternary complex. Two of the three chromatographically resolvable forms of the enzyme have been tested and found to have anticooperative behavior.

Animals↗
PubMed1975

Regulation of Escherichia coli glutamine synthetase. Evidence for the action of some feedback modifiers at the active site of the unadenylylated enzyme.

The interaction of unadenylylated form of Escherichia coli glutamine synthetase with several substrates and effectors has been examined by magnetic resonance techniques. These studies show that two manganese ions bind per enzyme subunit. From the dramatic line broadening observed in the alanine spectra in the presence of manganese and enzyme, it is concluded that the binding of alanine occurs at a site nearer one of the two manganese sites. Electron spin resonance (ESR) titration experiments suggest apparent dissociation constants of 20 and 120 muM for manganese to these sites in the presence of 1.0 mM magnesium ion. The manganese concentration dependence of the broadening of alanine suggests an affinity of 30 muM for the manganese closest to the alanine binding site. This suggests that alanine binds closer to the more tightly bound manganese ion. Glutamate appears to displace the alanine and also appears to bind close to the strongly bound manganese ion. It is proposed that alanine and glutamine bind competitively and in the same site. The binding of alanine and ATP is shown to thermodynamically interact such that the presence of one ligand increases the affinity of the enzyme for the other ligand. The presence of ATP dramatically sharpens the alanine line width when manganese and glutamine synthetase are present. Addition of ADP or phosphate alone has little effect on the alanine line width but the addition of both ADP and phosphate shows the same dramatic sharpening as the addition of ATP alone, suggesting an induced fit conformational change in the enzyme induced by ATP or by both ADP and phosphate. A binding scheme is proposed in which all feedback inhibitors of the enzyme bind in a competitive fashion with substrates.

Adenosine Diphosphate↗
PubMed1969

The use of nuclear magnetic resonance to describe relative modes of binding to lysozyme of homologous inhibitors and related substrates.

Proton magnetic resonance has been used to study the association of inhibitors and substrates with hen egg-white lysozyme. Changes in chemical shift, due to association, of acetamido methyl group resonances of the small molecules have been quantitated. This has allowed definition of magnetic parameters for three contiguous binding subsites on the enzyme surface. The relative modes of occupancy of these sites by N-acetyl-D-glucosamine (NAG), chitobiose, chitotriose, their methyl glycosides, and chitotetraose have been delineated. In addition, the binding to these sites of N-acetyl-D-muramic acid (NAM) and a cell-wall disaccharide, NAG-NAM, have been studied. There is good, although not complete, agreement between the results obtained and X-ray analysis studies of the binding of some of these inhibitors to crystalline lysozyme. Binding of synthetic substracts, such as p-nitrophenyl-2-acetamido-4-O-(2-acetamido-2-deoxy-beta-D -glucopyranosyl)-beta-D-glucopyranoside (NAG-Gluc-varphiNO(2)), has also been studied by the magnetic resonance technique described.

Binding Sites↗