In a permeabilized axon model, exogenous ATP can reactivate intraaxonal saltatory organelle movements (microscopically visible manifestations of fast axonal transport). We have studied the dependence of the reactivated movements on the ATP concentration and have also examined the nucleotide specificity of the reactivation. Organelle transport was visualized in isolated lobster giant motor axons using Nomarski optics and video microscopy. The axons were permeabilized with saponin, and movement was reactivated with ATP or other nucleotides. Some slight movement was seen with ATP concentrations as low as 10 microM. The velocity and frequency of the reactivated transport increased with increasing ATP concentrations up to about 5 mM. Movement was also reactivated by deoxyadenosine triphosphate, but not by AMP-PNP (a nonhydrolyzable ATP analogue), ADP, or AMP. Although other nucleotides (CTP, GTP, UTP, ITP) could reactivate transport, movement equivalent to that produced by 0.1 mM ATP was only seen with tenfold or greater concentrations of the other nucleotides. This pattern of specificity is consistent with the hypothesis that a dynein-like ATPase, rather than a myosin, is involved in fast axonal transport.

Described in a fast screening assay for aid in the differentiation of bacterial genera. Salmonella is separated from Escherichia and Shigella, as a generic group on the basis of an inhibition assay incorporating beta-2-thienylalanine, and using a defined medium. The assay is also usable for confirmation of taxonomic differences between genera. The inhibition reaction, readable as an 'all-or-none' phenomenon, follows a dose-response relationship for cultures affected by beta-2-thienylalanine, and is unaffected by the growth phase of the culture.

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Summary.Variation in the inhibition of growth of Escherichia coli and Shigella sp. in various media containing p-2-thienylaIanine was attributed to differences in concentrations of Mg+ + ions.Random blood samples from 112 infants were tested for elevated phenylalanine in the phenylketonuria (PKU) screening assay. Magnesium ion levels also affected the results of this assay. At 0 05 g/1 MgSO^, the concentration present in commercial PKU test agar, four false positives were detected, while no readings could be made due to overgrowth of the Bacillus suhtilis test strain when the concentration was increased to O'l g/1.INTRODUCTION.