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Biomedical subjects

S J Johnson

Publications and source records attributed to S J Johnson.

66 records · Page 4Linked to original sources
PubMed1982

The toxicity of jute (Corchorus olitorius) seed to pigs.

Finely ground Corchorus olitorius seed was administered as a daily drench to 1 pig at 100mg/kg body weight and as a single drench to 2 pigs at 500 mg/kg body weight. The latter 2 died within 48 hours, and the former was killed on the 7th day as it approached a moribund state. Clinical signs observed were anorexia, vomiting and dysentery. Autopsy revealed severe haemorrhagic enteritis. The seed was also fed to pigs at levels of 0.05%, 0.1% and 0.5% by weight of the ration for 4 weeks. Levels of 0.05% of greater caused reductions in voluntary feed intake and weight gain.

Animals↗
PubMed1982

Purification and characterization of dihydrofolate reductase from Walker 256 carcinosarcoma.

Dihydrofolate reductase of Walker 256 carcinosarcoma has been purified to homogeneity by affinity chromatography. The enzyme reduced 28 mumol dihydrofolate (FAH2) . min-1 . mg protein-1 at 22 degrees C and pH 7.3. Km values with respect to FAH2 and NADPH were 21 and 29 mM, respectively. The IC50 (amount of inhibitor required for 50% loss of enzyme activity) values were 0.2 nM for MTX and aminopterin and 50 and 67 nM, respectively, for N10-formyl FA and triazinate (NSC-139105). The pH maximum is around pH 7.0 and the isoelectric point is 6.8. This reductase has an apparent molecular weight of 21 500. The N-terminal amino acid is valine and the comparison of the N-terminal 20 residues of this reductase shows very high sequence homology with other mammalian reductases. The enzyme contains two cysteine residues and one of these residues is not involved in catalysis. This reductase has four tryptophan residues and modification of one of these residues leads to loss of activity. The intrinsic circular dichroic (CD) spectrum of this reductase is very different from the CD spectra of reductase of Escherichia coli B and L1210/MTX. However, the CD spectra of the enzyme--substrate and enzyme--inhibitor complexes are very similar to that of the L1210/MTX enzyme. This suggests that the ligands may be constrained in similar conformation on the two enzymes. The fluorescence emission maximum at 314 nM when activated at 286 nM is considerably lower than other mammalian enzymes.

Animals↗
PubMed1981

Stephanofilariasis in cattle.

A species of Stephanofilaria closely resembling S. stilesi is recorded as the cause of lesions on the head, neck and sternum of cattle in northern Queensland. Macroscopic and histopathological description of the lesions are given, together with a brief description of the parasite.

Animals↗
PubMed1980

Procion dyes as affinity ligands and reporter groups for dihydrofolate reductase from Walker 256 carcinoma.

Procion dye - agarose matrices were investigated for isolation of dihydrofolate reductase (FAH2R) from Walker 256 carcinosarcoma. Cibacron blue F3GA, Procion blue MX4GD, Procion blue HERD, and Procion red H3BN covalently bound to agarose adsorbed greater than 85% of pure FAH2R from 100 mM imidazole buffer, pH 6.3, and this enzyme was specifically and quantitatively eluted with 1 mM folate. The capacity and selectivity of the dye-agarose matrices were greater at low dye incorporation. Difference spectroscopy of the FAH2R - Cibacron blue F3GA complex indicated that 2 mol of the dye were bound in hydrophobic environments with each mole of the enzyme. NADPH and folate (at twofold molar excess over enzyme) or 1 M KCl displaced only 1 mol of Cibacron blue F3GA. This dye interacted stoichiometrically in a specific manner with the active site of FAH2R probably spanning the folate and NADP binding sites. The second dye molecule appears to be bound in a nonspecific hydrophobic manner. Selected Procion dye - agarose matrices can be used for partial purification of FAH2R from tumor homogenate.

Animals↗
PubMedDate not supplied

Pulmonary and neurobehavioral effects of formaldehyde exposure.

Two groups of male workers who were exposed to formaldehyde, the first group in phenol-formaldehyde-plastic foam matrix embedding of fiberglass (batt making), and the second in the fixation of tissues for histology, were studied for work-related neuro-behavioral, respiratory, and dermatological symptoms; and for pulmonary functional impairment. Forty-five male fiberglass batt makers who were studied across the initial work-shift after a holiday had average frequencies of combined neurobehavioral, respiratory, and dermatological symptoms of 17.3 for the hot areas and 14.7 for the cold areas of the process. Their symptom counts were significantly greater than those for 18 male histology technicians who averaged 7.3, and for 26 unexposed male hospital workers who averaged 4.8. During their first workshift after holidays, 58% of the batt makers had a decrease in one or more tests of pulmonary function. Nine nonsmokers had decreases more frequently than did 35 smokers; forced expiratory volume in one second FEV1.0 decreased in 16%, diffusing capacity for carbon monoxide (sb) decreased in 30%, forced expiratory flow 25-75 decreased in 16%, and forced expiratory flow) 75-85 decreased in 36%. Thirty-five percent of all 44 men had drops in FEV1.0, forced vital capacity, or in diffusing capacity (sb).

Adult↗
PubMedDate not supplied

Auditory brain stem response testing in infants with collapsed ear canals.

Auditory brain stem response (ABR) testing can provide valuable information about hearing in neonates. However, it is subject to a number of interpretive errors, not all of which have yet been resolved. Collapsing ear canals are one of these, as this report documents. We hypothesize that the quite common incidence of canal collapse in this age group, along with other transient conductive defects, may help to explain the 1:10 and 1:20 incidences of significantly abnormal ABRs in neonatal screening.

Brain Stem↗