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At least 109 records · Page 6Linked to original sources
PubMed1977

Estimation of the degree of crystallinity in digoxin by X-ray and infrared methods.

The X-ray procedure for estimation of the degree of crystallinity in digoxin is based upon measurement of the total X-ray scattering and the scattering from crystalline regions of the drug. The infrared procedures are based upon measurement of the peak height ratios, 1775/1618 and 3095/1618 cm-1. Correlation between results obtained by the two methods is good. These methods are of value in the physico-chemical characterization of digoxin, particularly as the properties may be altered by comminution.

Chemical Phenomena↗
PubMed1977

Dihydrofolate reductase: x-ray structure of the binary complex with methotrexate.

A central eight-stranded beta-pleated sheet is the main feature of the polypeptide backbone folding in dihydrofolate reductase. The innermost four strands and two bridging helices are geometrically similar to but are connected in a different way from those in the dinucleotide binding domains found in nicotinamide-adenine dinucleotide-linked dehydrogenases. Methotrexate is bound in a 15-angstrom-deep cavity with the pteridine ring buried in a primarily hydrophobic pocket, although a strong interaction occurs between the side chain of aspartic acid 27 and N(1), N(8), and the 2-amino group of methotrexate.

Binding Sites↗
PubMed1975

Relevance of three-dimensional reconstructions of stain distributions for structural analysis of biomolecules.

The relevance of a three-dimensional model of a protein molecule is discussed in the context of artefacts which inevitably occur during the preparation and imaging process. It is emphasized that even under optimistic assumptions, there-construction of a structure complementary to a given spatial stain distribution cannot, at resolutions below 10-15 A, be regarded as being identical with the real protein structure.

Glutaral↗
PubMed1975

Reprecipitation during the preparation of demineralized sections. II. Experimental observations.

Teeth were incompletely demineralized by immersion in unchanged 10% formic acid for 7 days. Reprecipitation deposits of secondary calcium phosphate were present in the dentin and soft tissues of the dental pulp and, if the final pH was 3 or greater, in the remnants of the periodontal ligament. The deposits in the dentin appeared to be intratubular. Deminieralized sections of teeth suspended in supersaturated solutions of brushite contained similar deposits in the soft tissues. It is suggested that reprecipitation of secondary calcium phosphates is a frequent intermediate stage during demineralization with formic acid.

Acids↗
PubMed1977

[Diffuse x-ray wide-angle scattering of polyglutamic acid in solution].

The diffuse wide angle x-ray scattering (WAXS) of polyglutamic acid (PGA) in solution was studied using an x-ray diffractometer with small aperture of the primary beam. The scattering curve was recorded at an angular interval from (article: see text). The experimental scattering intensity of PGA with alpha-helical CD spectrum showed a maximum at 14.4 nm-1. Unordered PGA in solution yielded no maximum at this scattering angle. The studies have proved that the scattering theory can be applied to globular proteins in solution as well as to chain molecules in solution in this angular interval. The differences between the calculated scattering curves and the experimental curves indicate minor movements of the side chains of PGA in solutions and slight structuring of the solvent at the surface of the polypeptide chain.

Glutamates↗
PubMed1978

Crystallographic studies on D-amino acid oxidase.

D-amino acid oxidase, a flavoprotein from hog kidneys, has been crystalized in two different forms. Orthorhombic prisms have been obtained from the enzyme.benzoate complex at pH 8.3; the space group is C2221 and the cell dimensions are a = 325A, b = 138.8 A, c = 200 A. At lower pH values, the enzyme crystallizes in trigonal prisms with a = b = 116.0 A, c = 399 A, space group P3112 or its enantiomorph. The two crystal forms have been obtained at 28 degrees C while at 4 degrees C only weak evidence of crystallization has been detected. In both crystalline modifications, the protein is highly associated.

D-Amino-Acid Oxidase↗
PubMedDate not supplied

[DNA complexes with lysozyme].

Sedimentation method has been used to study hen egg-white lysozyme binding to glucosylated (from T2 phage) and non-glucosylated (from calf thymus) DNA under conditions similar to physiological ones (pH 7,3--7,4, ionic strength 0.07--0.24). The results indicate that lysozyme binds cooperatively to both DNA's. Binding parameters have been obtained by applying the theory of one-dimensional adsorption of small molecules on a linear homopolymer. X-ray patterns of complexes with different protein content have been obtained.

Animals↗