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A N Schechter

Publications and source records attributed to A N Schechter.

At least 181 records · Page 10Linked to original sources
PubMed1974

The active site of staphylococcal nuclease: paramagnetic relaxation of bound nucleotide inhibitor nuclei by lanthanide ions.

The structure of 3',5'-thymidine diphosphate bound in the active site of staphylococcal nuclease (EC 3.1.4.7) was studied by measuring the relaxation rate enhancement of substrate analog nuclei by a paramagnetic metal ion. The lanthanide ion, Gd(III), was substituted for Ca(II) in the formation of the ternary complex of nuclease-Gd(III)-3',5'-thymidine diphosphate. Measurements were made of the transverse relaxation rates of protons and the longitudinal and transverse relaxation rates of the phosphorus nuclei of the bound nucleotide. Internuclear distances between the metal ion and atoms of the 3',5'-thymidine diphosphate nucleotide were determined from these data by the Solomon-Bloembergen equation. In general, these distances corresponded closely to those determined by previous x-ray crystallography of the thymidine diphosphate complex.These internuclear distances were also used with a computer program and graphics display to solve for metal-nucleotide geometries, which were consistent with the experimental data. A geometry similar to the structure of the metal-nucleotide complex bound to nuclease determined by x-ray analysis was one of the solutions to this computer modeling process. For staphylococcal nuclease, the nuclear magnetic resonance and x-ray methods yield compatible high resolution information about the structure of the active site. However, differences of uncertain significance exist between the two structures.

Binding Sites↗
PubMed1972

An immunologic approach to the conformational equilibria of polypeptides.

Antibodies reactive with distinct regions of the staphylococcal nuclease molecule were prepared both by immunization with polypeptide fragments of nuclease and by immunization with intact nuclease followed by fractionation of the antiserum on immuno-absorbent columns bearing the corresponding fragments. Comparisons of the interactions of these antibody preparations with nuclease, by quantitative precipitin assays and enzyme inhibition studies, showed marked differences attributable to the conformation of the immunizing antigens. An interpretive model is proposed in which antibodies fractionated from anti-nuclease serum react effectively only with the "native format determinants" of polypeptide fragments of nuclease. It is postulated that such determinants are generated in polypeptide fragments by spontaneous and reversible folding of the polypeptide chain. The model permits experimental determination of parameters, K(conf), for the proposed conformational equilibria.

Animals↗
PubMed1971

Folding of staphylococcal nuclease: magnetic resonance and fluorescence studies of individual residues.

The reversible unfolding and folding of staphylococcal nuclease in the acid transition has been studied by 220 MHz proton magnetic resonance spectroscopy. The values of area, line-width, and chemical shift of each of the imidazole C2 proton resonances of the four histidine residues have been measured in this transition. The change of areas of three histidine resonances and the change of fluorescence of the single tryptophan residue, as a function of pH, appear to follow a single equilibrium. In contrast, a fourth histidine resonance follows a biphasic transition. These findings indicate that local conformational changes can be detected by magnetic resonance spectroscopy in the cooperative transition of the overall structure.

Amino Acid Sequence↗