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B B Kitchell

Publications and source records attributed to B B Kitchell.

22 records · Page 2Linked to original sources
PubMed1978

Effect of temperature on fluorescence and circular dichroism of Escherichia coli dihydrofolate reductase and its complexes.

Dihydrofolate reductase and its complexes have been studied by fluorescence and circular dichroism. NADPH, trimethoprim, pyrimethamine, or Methotrexate binding causes small changes in the enzyme far ultraviolet CD which possibly arise from alterations in polypeptide backbone of the enzyme; however, their effects on enzyme far ultraviolet CD are also explained as the result of ligand interactions with enzyme aromatic groups. In ternary complexes of the enzyme, fluorescence properties of bound NADPH are surprisingly sensitive to the type of inhibitor bound nearby. The effect of temperature on the enzyme and its complexes is clearly shown by changes in enzyme fluorescence and CD. At temperatures near 45 degrees C, the enzyme undergoes an irreversible denaturation, as shown by major alterations in enzyme far ultraviolet CD and by an increased rate of fluorescence quenching. Binary complexes with NADPH or Methotrexate stabilize the enzyme towards this heat denaturation, whereas bound trimethoprim and pyrimethamine do not. Ternary complexes with NADPH and any of the ligands are more stable than the enzyme itself toward heat denaturation. Fluorescence-temperature and fluorescence polarization studies show that near 30 degrees C the enzyme undergoes a reversible transition that is modified by NADPH or methotrexate.

Circular Dichroism↗
PubMed1977

Optical and hydrodynamic studies of the structure of bacteriophage f2. II. Fluorescence of the capsid.

Fluorescence properties of the icosahedral RNA virus bacteriophage f2 and its empty capsid are reported. Emission is dominated by tryptophan with a maximum wavelength of 320 nm for f2 and its empty capsid. In addition to this short wavelength maximum, perturbation and denaturation studies indicate the inaccessibility of the tryptophan residues. However a high degree of thermal quenching and a red shift in fluorescence emission on heating suggest a noncooperative structural transition, not a denaturation, which allows buried tryptophans to become exposed to solvent. Therefore the tryptophan residues may be located between subunits. Fluorescence from tyrosine is detected near 315 nm for both f2 and its empty capsid, and may indicate an unusual tyrosine environment. Sensitization of tryptophan fluorescence by tyrosine absorption and low values of polarization indicate tyrosine leads to tryptophan and tryptophan leads to tryptophan energy transfer. The presence of RNA in f2 decreases the efficiency of these transfer processes, but does not significantly affect the other reported fluorescence properties.

Capsid↗