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Biomedical subjects

R A Day

Publications and source records attributed to R A Day.

At least 37 records · Page 2Linked to original sources
PubMed1985

Cyanogen-induced gamma-glutamyl to imidazole cross-link in carbonic anhydrase. A unique mode of inhibition.

The irreversible inhibition of carbonic anhydrase by cyanogen occurs by a unique mechanism. Cyanogen is an affinity label: it behaves like a carbodiimide and produces an intra-molecular cross-link without being incorporated. The nucleophile-labile cross-link is formed between a gamma-COOH of a Glu and an imidazole of a His with a 1:1:1 stoichiometry with the enzyme. The deletion of approximately 1 Glu and approximately 1 His was noted by amino acid analysis of enzymatically hydrolyzed carbonic anhydrase. The modified Glu was converted to 2,4-diaminobutanoic acid and quantitated by amino acid analysis. The presence and quantity of modified His was supported through high-resolution proton NMR analysis.

Amino Acids↗
PubMed1985

Irreversible inhibition of carbonic anhydrase by the carbon dioxide analog cyanogen.

Cyanogen (C2N2), a molecule with properties remarkably similar to carbon dioxide, differentially inhibits three of the four carbonic anhydrases reported here. Bovine carbonic anhydrase II shows 97% loss of esterase activity with no concommitant loss in hydratase activity. The hydratase and esterase activities of human carbonic anhydrase I are decreased by 80% and 55% respectively. Canine carbonic anhydrase shows similar results to human carbonic anhydrase I, retaining 29% hydratase and 62% esterase activity. Rabbit carbonic anhydrase sustained no loss of either hydratase or esterase activity. This inhibition occurs by an irreversible modification of the enzymes. The kinetic parameters for modified and unmodified enzymes were altered in a way that reflects the characteristic effect for each carbonic anhydrase.

Acetates↗
PubMed1984

A polycationic amine that induces unique conformational changes in poly(dA-dT) in low salt.

Circular dichroism was used to examine alterations in the secondary structure of poly(dA-dT) X poly(dA-dT) upon binding polymer X, a polycationic CD probe for aspects of DNA structure. Stable complex formation is evidenced by increasing Tm and the appearance of large extrinsic bands in the greater than 300 nm, region which increase proportionally with r (ratio of polymer charge to DNa phosphate), in the range 0.0 to 0.32. At relatively low values of r (less than .32), CD spectra of the poly(dA-dT) X poly(dA-dT)-polymer X complex show a gradual non-cooperative inversion in the long wavelength portion (275 nm) of the intrinsic band in low salt solutions suggesting structural and conformational flexibility in poly(dA-dT) X poly(dA-dT) and further implicating polymer X as a potential probe for variations in DNA secondary structure. The dinucleotide repeat configuration of poly(dA-dT) X poly(dA-dT) is presumed to play a role in the observed intrinsic CD changes. NMR data support an "alternating B" conformation for the complex.

Circular Dichroism↗
PubMed1983

Bacillus cereus 569/H penicillinase serine-44 acylation by diazotized 6-aminopenicillanic acid.

Penicillinase from Bacillus cereus 569/H was purified to homogeneity. Its active site was probed by use of an affinity label generated in situ by the diazotization of 6-aminopenicillanic acid, a catalytically poor substrate for this enzyme. The loss of activity arising during the inactivation is dependent upon pH and the penicillin:sodium nitrite ratio used. Optimal inactivation was obtained at pH 4.7 and reactivation could be prevented if subsequent purification and manipulations were performed at low pH. Inactivation by diazotized 6-aminopenicillanic acid was characterized further by tryptic and chymotryptic digestion of the inactivated enzyme and peptide mapping of the resulting digests. Amino acid analysis of the chymotryptic labeled peptide yielded a composition which corresponds to residues 41-46 (Ala-Phe-Ala-Ser-Thr-Tyr) in the published partial sequence of the enzyme (Thatcher, D. (1975) Biochem. J. 147, 313-326). Further digestion of this chymotryptic peptide with carboxypeptidase A reveals that serine-44 is modified in this affinity labeling procedure. Mass spectral analysis of the modified serine residue and alkali-released label, and comparison with spectra of model compounds indicates that the inactivation occurs with rearrangement of the beta-lactamthiazolidine structure to a dihydrothiazine.

Acylation↗
PubMed1979

Comparison of holdings of NLM (CATLINE) with those of resource libraries.

The collection development practices of the National Library of Medicine (NLM), with the goal of comprehensive acquisition of biomedical monographs, are compared with those of the resource libraries of the TALON (Region IX) Regional Medical Library. Holdings of two resource libraries in the TALON region, The University of Texas Health Science Center at San Antonio and The University of Texas Medical Branch at Galveston, and of the TALON Union Catalog of Monographs were compared with the NLM CATLINE data base for four subject classes and selected imprint years. Foreign-language coverage is lacking in Region IX, with English-language coverage is lacking in Region IX, with English-language coverage ranging between 70 and 88% of titles listed in CATLINE. Absent English-language material tends to be ephemeral or otherwise out of scope for the resource libraries. Between 7.1 and 18.8% of monographs acquired in each subject class by the two recource libraries are lacking in CATLINE; this represents between 2 and 8% of the CATLINE titles for each class.

Book Collecting↗
PubMed1976

The pH dependence of binding of alpha,alpha'-dibromo-p-xylenesulfonic acid to lysozyme.

The chemical modification of lysozyme (I) has been accomplished with alpha, alpha'-dibromo-p-xylenesulfonic acid (DBX) at five different pH values. I was alkylated by DBX at room temperature (28 degrees C) with decrease in enzyme activity. The rate of inactivation depended upon the pH at which alkylation was carried out. The highest rate was seen at alkaline pH values; the lowest at more acidic pH values. Amino acid analyses showed that-two lysines and two tryptophan residues had been modified at pH 9; two lysines, one tryptophan and one methionine had reacted at pH 8. A histidine residue was bound at pH 6.5 together with a tryptophan residue. At the lower pH values (2.7, 4.5, 6.5), alkylation occurred with a single tryptophan residue each. Fluorescence and CD data both ruled out the participation of tryptophans 62 or 108. Labeling experiments showed that two residues of DBX-35S were bound per molecule of I at both pH9 and pH8; one residue of DBX was bound per molecule of I at the other pH values. Sedimentation coefficients were characteristic of native lysozyme. The stoichiometry of binding and residue modification indicated that intra-molecular cross links were established. The pH dependence of the cross-linking provides means to measure several allowed intra-molecular distances. The results presented here are consistent with the existence of side chain motion in lysozyme.

Amino Acids↗
PubMed1975

A Hg (II) induced conformational change in penicillinase.

Penicillinase (E.C. 3.5.2.6) from Bacillus cereus 569/H is inhibited by Hg(II). The inhibition is characterized by non-competitive kinetics and can be reversed by EDTA. A Hg(II) induced conformational change is indicated because: (1) The EDTA regenerated activity is unstable and is rapidly converted to an iodine-sensitive state, and (2) An irreversible change in the circular dichroism spectrum at 222 nm is found.

Bacillus cereus↗