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Biomedical subjects

B J Johnson

Publications and source records attributed to B J Johnson.

At least 127 records · Page 7Linked to original sources
PubMed1977

An 125I radioimmunoassay for primary conjugated bile salts.

Cholylglycylhistamine, a derivative of cholic acid, has been synthesized and characterized. This derivative has been iodinated using Na125I and chloramine-T and purified free from unlabeled cholylglycylhistamine. Application of this iodinated bile salt derivative to radioimmunoassay of bile salts in human serum is reported. Antibody titers have uniformly increased over titers used in tritium-based assays; some antibodies are usable in dilutions of 1:80,000. The radioimmunoassay described here was found to measure predominantly the primary conjugated bile salts. Sensitivity has been maintained, with the least detectable amount being 0.5 pmoles per assay tube. Normal values in human serum are 3.47 +/- 2.16 (SD) nmoles per ml.

Animals↗
PubMed1976

Lipid-protein interactions: enhancement of enzyme activity of L-glutamic acid dehydrogenase by nonionic detergents.

Five nonionic detergents enhanced the activity of L-glutamic acid dehydrogenase [L-glutamate:nicotinamide adenine dinucleotide phosphate oxidoreductase (deaminating) (EC 1.4.1.3)]. These detergents activated the enzyme toward alpha-ketoglutaric acid reduction, causing a decrease in the sensitivity of the enzyme to allosteric regulation by guanosine 5-triphosphate. There was also a diminution of the enhancing effect of the modifier adenosine 5-diphosphate on the enzyme's L-glutamic acid dehydrogenase activity. These detergents may cause a conformational change in the enzyme, and this change could lead to an increase in the binding of the substrates for the alpha-ketoglutaric acid reduction. Accompanied with this conformational change would be a decrease in the binding of the modifier guanosine 5'-triphosphate, with no concomitant change in the binding of the adenosine 5'-diphosphate modifier.

Adenosine Diphosphate↗
PubMed1976

Investigations of the complement-fixing sites of immunoglobulins.

Indirect evidence for the complement-fixing site of human IgG1 has been found by using chemical modification of the immunoglobulin. These results implicate the amino acid residues, tryptophan, tyrosine, and arginine. Furthermore, by the use of synthetic peptides it has been shown that the area surrounding the tryptophan and tyrosine at positions 277 and 278 probably constitutes the locus of the complement-fixing site of human IgG1. By analogy, the tryptophan at position 488 of human IgM is implicated in the complement-fixing site of this immunoglobulin. Evidence for this is presented by a peptide which mimics the sequence 487-491 of human IgM and possesses the ability to consume complement. The relative complement-fixing ability of this peptide is 200 times less effective than human IgG1.

Amino Acid Sequence↗
PubMed1976

Studies on the antigenic determinants of the Thy-1.2 alloantigen as expressed by the murine lymphoblastoid line S-49.1 TB-2-3.

Sialic acid has been shown to be part of the antigenic determinant of the Thy-1.2 alloantigen as expressed by the murine cell line S-49.1 TB-2-3 (S-49). This conclusion is based on the loss of cytotoxic inhibitory activity by the action of neuraminidase on the Thy-1.2 alloantigen. Also, sialic acid has the ability to inhibit the cytotoxic assay of AKR anti-C3H Thy-1.2 serum for S-49 cells. Further evidence for the protein nature of the Thy-1.2 alloantigen is apparent by trypsin digestion. Possibly the Thy-1.2 alloantigen as expressed on S-49 cells is a glycoprotein.

Animals↗
PubMed1975

The protein nature of the Thy-1.2 alloantigen as expressed by the murin lymphoblastoid line S-49.1 TB-2-3.

This preliminary study was undertaken to investigate the chemical nature of the Thy-1.2 antigen expressed on the murine cell line S-49.1 TB-2-3 (S-49). The presence of the Thy-1.2 antigen was indicated by the inhibition of AKR anti-C3-Thy-1.2 serum induced lysis of 51Cr-primed target cells. It was found that limited digestion of S-49 cells with crude papain yielded a Thy-1.2-containing solution. The protein nature of the Thy-1.2 antigen obtained in this manner was indicated by changes after proteolytic digestion. Separate digestions with crystalline papain, insolubilized papain, and insolubilized protease all destroyed the Thy-1.2 activity. These results suggest that the protein moiety is necessary for Thy-1.2 activity.

Absorption↗