Choline acetyltransferase activity of spinal cord cell cultures is increased by diisopropylphosphorofluoridate.

Diisopropylphosphorofluoridate (DFP) increased the specific activity of choline acetyltransferase (ChAT) in mouse spinal cord cell cultures but paraoxon did not, though both toxicants inhibited cholinesterase activity to a comparable extent. This effect of DFP was observed after prolonged exposure but not after short-term application to the cultures. It is postulated that this delayed effect of DFP $\text{in vitro}$ may possibly be related tothe delayed neuropathy caused by DFP in certain species $\text{in vivo}$.     

Inhibition of mammalian deoxyribonucleic acid synthesis by neocarzinostatin: selective effect on replicon initiation in CHO cells and resistant synthesis in ataxia telangiectasia fibroblasts

Treatment of CHO cells with low doses of the protein antibiotic neocarzinostatin severely inhibited DNA replicon initiation but had no effect on chain elongation. The selectivity of the effect on initiation, which was greater than that seen with other chemical agents and comparable to that seen with X-rays, explains the biphasic dose response seen for DNA synthesis inhibition by this drug. Parallel experiments employing the nucleoid sedimentation technique indicated that half-maximal relaxation of domains of DNA supercoiling and half-maximal inhibition of replicon initiation required the same dose of neocarzinostatin, approximately 0.03 micrograms/mL. These results, similar results obtained with the protein antibiotic auromomycin, and previous results obtained with X-rays suggest a quantitative correlation between inhibition of replicon initiation and induction of sufficient strand breakage to relax domains of supercoiling in DNA of mammalian cells. Results in human ataxia telangiectasia fibroblasts indicated that neocarzinostatin, like X-rays, is much less effective in inhibiting DNA synthesis in these cells than in normal human fibroblasts. This finding is consistent with the hypothesis that the genetic defect in ataxia telangiectasia involves a failure to recognize the presence of strand breaks in cellular DNA.     

Properties of recombinant cells capable of growing on serine without NhaB Na+/H+ antiporter in Escherichia coli.

Escherichia coli HIT-1 has a mutation in the Na+/H+ antiporter gene, nhaB (P. Thelen, T. Tsuchiya, and E. B. Goldberg, J. Bacteriol. 173:6553-6557, 1991). This strain is not able to utilize serine as a carbon source (T. Ishikawa, H. Hama, M. Tsuda, and T. Tsuchiya, J. Biol. Chem. 262:7443-7446, 1987), because an active NhaB is required to maintain the electrochemical potential of Na+, which drives serine transport via the Na+/serine carrier, the major transport system for serine. We isolated recombinant cells from a cross between strains HIT-1 and Hfr, and these cells were able to grow on serine even though the NhaB Na+/H+ antiporter of the recombinant cells was still defective. We found that the activity of the H+/serine cotransport system, one of the minor serine transport systems in E. coli, was elevated in the recombinant cells. H+/serine cotransport activity was induced by leucine in the recombinant cells more strongly than in strain HIT-1. A kinetic analysis showed that the Vmax, but not the Km, of the transport system was much higher in the recombinant cells than in strain HIT-1 cells.     

Quantification and excretion profiles of pteridines in primate urine.

Biopterin, 6-hydroxymethyl-pterin, isoxanthopterin, neopterin and, pterin were quantified in stress-free collected spontaneous morning urine samples from Callithrix jacchus, Saguinus fuscicollis, Saguinus labiatus, Saimiri sciureus, Presbytis entellus, Cercopithecus albogularis, Cercocebus torquatus, Macaca fascicularis, Hylobates concolor, Pongo pygmaeus, and Gorilla gorilla. In most species, biopterin was the most frequent urinary pteridine followed by neopterin. Sex differences in biopterin and neopterin excretion were observed in Gorilla gorilla and Pongo pygmaeus. Pterin and isoxanthopterin were only present in minor concentrations. 6-hydroxymethyl-pterin was barely detectable and not present in the urine of Saguinus labiatus, Saimiri sciureus, and both male Gorilla gorilla and Pongo pygmaeus.