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T B Johnson

Publications and source records attributed to T B Johnson.

32 records · Page 2Linked to original sources
PubMed1970

The Active Site on the Phytotoxin of Corynebacterium sepedonicum.

Corynebacterium sepedonicum produces an extracellular phytotoxic glycopeptide that possesses a capacity to wilt plant cuttings. It has been previously demonstrated that the integrity of some of the membranes of the host cells is destroyed, suggesting the possibility that a biologically active site is present on the toxin molecule. The toxin was chemically altered in the following ways and then tested for biological activity: (a) the NH(2)-terminal group on the peptide portion of the toxin was blocked by the dansylation technique; (b) the OH groups on the sugar and amino acid residues as well as the NH groups on the amino acid residues were blocked by exhaustive methylation; (c) the COO(-) groups were converted to their respective methyl esters; (d) the peptide moiety was removed by pronase digestion. Experimental results indicate that the carboxyl groups of the nonpeptide portion of the molecule are responsible for the biological activity of the toxin. Other experiments showed that the toxin does not affect the membranes of animal cells.The biological activity of the glycopeptide, as well as its chemically altered derivatives, was determined by an instrument designated as a wilt-o-meter that quantitatively measures the strength of plant cuttings. A description of this instrument, how it is used, and how it can be manufactured is also included in this report.

Journal Article↗
PubMedDate not supplied

Neonatal binge ethanol exposure using intubation: timing and dose effects on place learning.

Neonatal rats were given ethanol using an acute intubation procedure that resulted in daily binge-like exposure with minimal effects on somatic growth. Acquisition of place learning in the Morris water maze was evaluated on postnatal days (PD) 26-31. In Experiment 1, a total of 5.25 g/kg/day of ethanol was administered in two daily intubations on PD 4-6, PD 7-9, or PD 4-9, producing mean peak BACs of 265 mg/dL. Place learning acquisition deficits in a 114-cm-diameter tank were found for the PD 4-9 and PD 7-9 groups, but not the PD 4-6 group. In Experiment 2, either 4.5 or 5.25 g/kg/day of ethanol was administered on PD 7-9 and place learning was tested in a 171-cm-diameter tank. Significant acquisition deficits resulted from the higher dose, and probe trial search patterns for both ethanol groups were significantly less localized than controls. In Experiment 3, no significant effects of either PD 7-9 dose were found on a visible platform task. These findings reveal selective place learning deficits in this intubation model of neonatal binge exposure, and confirm a temporal window of vulnerability to spatial learning deficits during the second neonatal week.

Animals↗