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Biomedical subjects

R A Day

Publications and source records attributed to R A Day.

51 records · Page 3Linked to original sources
PubMed1973

Penicillin-binding component of Bacillus cereus.

(14)C-penicillin is irreversibly bound by Bacillus cereus 569. Incubation of penicillin-treated cells in a cell wall digestion medium results in solubilization of approximately 60% of the irreversibly bound lable. The extent of the solubilization is the same when cells are prepared by either a cold or 37 C treatment procedure. However, spheroplasts prepared by the cold treatment are leaky. When the resulting spheroplasts are incubated in supplemented medium, reduced rates and levels of penicillinase synthesis, relative to induced whole-cell controls, are observed. Spheroplasts from both cold and 37 C prepared cells exhibit this phenomena, although the spheroplasts from 37 C prepared cells synthesized approximately sixfold higher levels of penicillinase. The size distribution of the label solubilized during the preparation of spheroplasts was examined by using Bio Gel P-150 columns. Although no label appeared in the exclusion volume fractions when the cell wall digest of the 37 C treated cells was chromatographed, approximately 10% of the label from cold-treated cells did appear. These results suggest that the presence of irreversibly bound penicillin is required for the synthesis of induced levels of penicillinase and that the irreversibly bound penicillin can be solubilized as a labile complex with material which is excluded from BioGel P-150. It may be concluded that the penicillin-binding lipoprotein complex which has been previously observed is the penicillin-specific binding site. However, the location of this complex in relation to the cell membrane could not be determined.

Amino Acids↗
PubMed1968

Photolytic cleavage of sulfonamide bonds.

It has been found that the sulfonamide bond is relatively susceptible to photolytic cleavage. The breakdown was effected either by irradiation with a source having a continuous emission above the wavelengths of 1800 angstroms or by another source emitting principally at 2537 angstroms. Less destruction of the amino acids was seen with the latter relative to the sulfonamide bond cleavage. The cleavage was not effected by irradiation at wavelengths greater than about 3000 angstroms. Side reactions were noted involving decarboxylation, demination, and destruction of certain susceptible amino acids such as tryptophan. In only one case was a product found that arose from cleavage of a carboxamide bond; glycyltyrosine gave glycine and tyrosine upon irradiation. A yield of 75 percent of the corresponding amino acid has been obtained by irradiation of tosylhistidine; yields of 75 to 100 percent have been obtained from sulfamic acid (NH(2)SO(3)H). A qualitative method for identifying sulfonylated amino acids is described.

Arginine↗
PubMed1968

Protein conformation in solution: cross-linking of lysozyme.

The cross-linking of lysozyme by reaction with phenol-2,4-disulfonyl chloride has been effected. The cross-linked protein retained enzymatic activity, has approximately the same molecular weight as native lysozyme, and has essentially the same conformation as native lysozyme as judged by optical rotatory dispersion analysis. The positions of sulfonylation were assigned by a standard degradation sequence; the presence of sulfonamide bonds was confirmed by infrared spectroscopy. Cross-links may thus be introduced without incurring major structural changes in the protein, and certain intramolecular distances that are allowed in the active enzyme may be deduced.

Amino Acids↗
PubMedDate not supplied

Creatinine, lactam and cyclic peptide formation by the action of C2N2 on creatine, omega-amino acids and peptides.

Cyanogen, C2N2, affords a means to drive intramolecular conversion of ammonium salts to amides. Unlike other carboxyl activating agents, such as carbodiimides, used in peptide syntheses expressly to drive intermolecular condensations to form amide (peptide) bonds, C2N2 appears restricted to driving only intramolecular condensations. Rates decreased as a function of solvent composition as follows: organic much greater than 70%-80% aqueous organic much greater than 50% aqueous organic greater than H2O. Temperature dependence was also a function of solvent composition. Rates did not strongly reflect steric constraints with beta-lactams and epsilon-lactams forming at comparable rates to rates for gamma- and delta-lactam formation; likewise L-Leu-L-Leu cyclized at about the same rate as L-Leu-D-Leu. Pro-Pro is well documented as having a salt-bridged structure in a variety of solvents where it cyclized extremely rapidly. The reaction is proposed to be dependent on reaction of C2N2 with salt-bridges on the basis of 1) its preponderant if not exclusively intramolecular nature, 2) its solvent dependence, 3) its temperature dependence and 4) the conversion of known salt-bridged structures to amides. This reaction is a model for the observed rapid reaction of salt bridges in proteins.

Amino Acids↗