PubMed Health⌕ Search

Biomedical subjects

H S Johnson

Publications and source records attributed to H S Johnson.

13 recordsLinked to original sources
PubMed1983

Characterization of monoclonal antibodies specific for the Lewis a human blood group determinant.

Four hybridoma cell lines were derived from the spleen cells of mice immunized with the neutral glycolipids of human meconium. The antibodies secreted by these lines were specific for the Lewis a antigen of the human Lewis blood group system as determined by solid phase immunoassay using synthetic carbohydrate antigens and by plate binding assay and thin layer chromatography-autoradiography using natural glycolipid antigens. Coating protein A-bearing Staphylococcus aureus with one of the antibodies yielded a stable reagent that produced rapid agglutination of Lewis a positive human erythrocytes. The fine structural specificity of these antibodies was assessed by competition radioimmunoassay using synthetic structural analogs of Lewis a conjugated to bovine serum albumin. One antibody was specific for the Lewis a trisaccharide (Gal beta 1 leads to 3(Fuc alpha 1 leads to 4) beta GlcNAc), while a second recognized the entire Lea (1 leads to 3) beta Gal tetrasaccharide. The third and fourth were directed at topography largely provided by only the alpha Fuc and beta GlcNAc units. These monoclonal antibodies not only represent potentially useful reagents for detecting the Lewis a antigen but also provide a system for studying precise relationships between anticarbohydrate antibody structure and binding specificity.

Animals↗
PubMed1983

Decreased glycolipid antigen expression in lymphoma cell variants escaping from anti-glycolipid serotherapy.

Mice challenged with L5178Y lymphoma cells expression high levels of the glycolipid asialo GM2 (gangliotriosylceramide) were protected from tumor growth by passive administration of a monoclonal antibody specific for the glycolipid; in a few antibody-treated mice, ascites cells eventually proliferated which contained a reduced chemical quantity of the glycolipid antigen (3). We now report that the cells emerging from antibody-treated mice had abnormal marker chromosomes identical to those in the cells used for challenge, indicating that the emergent cells were progeny of the challenge inoculum. Flow cytometric analysis revealed that asialo GM2 was undetectable on the surface of greater than 95% of the tumor cells from antibody-treated mice, whereas surface display of H-2 determinants was unchanged from that of the cells used for challenge. Tumor cells arising in challenged but untreated mice consisted of a mixture of asialo GM2-positive and -negative cells, indicating the presence of selective pressures in these mice as well. None of the cells taken from tumor bearing mice differed significantly from the challenge cells in their susceptibility to natural killer cell attack, suggesting that resistance to natural killer cell lysis was not responsible for the proliferation of these cells in vivo. When cells derived from an antibody-treated mouse were used to challenge mice, serotherapy with anti-asialo GM2 had no effect on mouse survival. These results suggest that serotherapy may complement a host anti-tumor response, from which only asialo GM2 deficient cells can escape.

Animals↗
PubMed1981

Minicolumn detection methods for aflatoxin in raw peanuts: collaborative study.

The Holaday-Velasco method and a modified Holaday method have been compared. The former method combines the speed and simplicity of the Holaday extraction and cleanup with the sensitivity of the minicolumn originally described by Velasco. The combination method has been approved by the AOAC and the AACC for determining aflatoxin in corn. The Holaday method was modified by substituting toluene for benzene in the solvent partition, and methylene chloride for chloroform in the minicolumn development to eliminate use of hazardous solvents. The neutral alumina in the Holaday minicolumn was changed from activity V to activity III to provide a more stable column. At aflatoxin levels in raw peanuts of 13-20 ng/g, the presence of aflatoxin was missed by the modified Holaday method in 4 analyses (3 laboratories) of 42 reported. There were no misses in this contamination range by the Holaday-Velasco method. There were no misses by either method with samples containing greater than 20 ng total aflatoxins/g. Analysis of uncontaminated raw peanuts by the modified Holaday method resulted in 2 false positives of 14 reports; the Holaday-Velasco method produced no false positive reports from 15 analyses of uncontaminated peanuts. The Holaday-Velasco method was adopted official first action for peanuts.

Aflatoxins↗
PubMed1970

Properties and regulation of leaf nicotinamide-adenine dinucleotide phosphate-malate dehydrogenase and 'malic' enzyme in plants with the C4-dicarboxylic acid pathway of photosynthesis.

1. NADP-malate dehydrogenase and ;malic' enzyme in maize leaf extracts were separated from NAD-malate dehydrogenase and their properties were examined. 2. The NADP-malate dehydrogenase was nicotinamide nucleotide-specific but otherwise catalysed a reaction comparable with that with the NAD-specific enzyme. By contrast with the latter enzyme, a thiol was absolutely essential for maintaining the activity of the NADP-malate dehydrogenase, and the initial velocity in the direction of malate formation, relative to the reverse direction, was faster. 3. For the ;malic' enzyme reaction the K(m) for malate was dependent on pH and the pH optimum varied with the malate concentration. At their respective optimum concentrations the maximum velocity for this enzyme was higher with Mg(2+) than with Mn(2+). 4. The NADP-malate dehydrogenase in green leaves was rapidly inactivated in the dark and was reactivated when plants were illuminated. Reactivation of the enzyme extracted from darkened leaves was achieved simply by adding a thiol compound. 5. The activity of both enzymes was low in etiolated leaves of maize plants grown in the dark but increased 10-20-fold, together with chlorophyll, when leaves were illuminated. 6. The activity of these enzymes in different species with the C(4)-dicarboxylic acid pathway was compared and their possible role in photosynthesis was considered.

Chlorophyll↗
PubMed1969

The C4-dicarboxylic acid pathway of photosynthesis. Identification of intermediates and products and quantitative evidence for the route of carbon flow.

1. When leaves with the C(4)-dicarboxylic acid pathway of photosynthesis are exposed to (14)CO(2) the major labelled compounds formed, in order of labelling, are dicarboxylic acids, 3-phosphoglycerate, bexose phosphates and sucrose. During the present studies several quantitatively minor intermediates were identified and their labelling behaviour is described. 2. The pattern of labelling of dihydroxyacetone phosphate, fructose 1,6-diphosphate and ribulose di- and mono-phosphates during radiotracer pulse-chase experiments was consistent with their operation as intermediates in the pathway of carbon dioxide fixation. 3. Serine, glycine, alanine and glutamate had labelling patterns typical of products secondary to the main flow of carbon. 4. The mechanism of the transfer of label from C-4 of dicarboxylic acids to C-1 of 3-phosphoglycerate was also examined. Evidence consistent with pyruvate being derived from C-1, C-2 and C-3 of oxaloacetate, and for a relationship between ribulose 1,5-diphosphate and the acceptor for the C-4 carboxyl group, was obtained. 5. Evidence is provided that, under steady-state conditions, essentially all the label incorporated from (14)CO(2) into C-1 of 3 phosphoglycerate enters via C-4 of the dicarboxylic acids. These and other studies indicated that the route via dicarboxylic acids is essentially the sole route for entry of carbon into 3-phosphoglycerate.

Amino Acids↗
PubMed1967

Further studies on a new pathway of photosynthetic carbon dioxide fixation in sugar-cane and its occurrence in other plant species.

1. The pathway of photosynthesis in sugar-cane, which gives most of the radio-activity fixed during short periods in (14)CO(2) in C-4 of oxaloacetate, malate and aspartate, was examined under varied conditions. 2. The pattern of labelling was essentially the same with leaves of different ages and with leaves equilibrated at carbon dioxide concentrations in the range 0-3.8% (v/v) and light-intensities in the range 1400-9000ft.-candles before adding (14)CO(2). 3. Radioactive products were examined after exposing leaves of 33 different plant species to (14)CO(2) for 4sec. under standard conditions. 4. A labelling pattern typical of sugar-cane was found in several species of Gramineae but not in others. Of 16 species from other Families only a species of Cyperaceae contained a large proportion of the fixed radioactivity in oxaloacetate, malate and aspartate.

Carbon Dioxide↗