Worm Breeder's Gazette 6(1): 37a
These abstracts should not be cited in bibliographies. Material contained herein should be treated as personal communication and should be cited as such only with the consent of the author.
Encouraged by Stretton & Co.'s result that many minutes are required to wash the muscle-contracting effect of meta-aminolevamisole out of Ascaris muscle strips, we've synthesized tritiated meta- aminolevamisole of high specific radioactivity. By thin layer chromatography, the drug is greater than 97% radiochemically pure, has the same high biological potency on cut C. elegans as the nonradioactive drug, and has a specific radioactivity of 15 to 30 Ci/mmole. We incubate the radioactive drug with total worm extract and collect any radioactivity bound to membrane fragments by passing the extract through a glass fiber fiIter. A control assay is done in the presence of a thousand fold excess of nonradioactive drug. Specific binding is the difference between the total binding (first assay) and nonspecific binding (second assay). We find that the wiId type nematode containing a high affinity, saturable binding activity. There is about 1 picomole of this activity per gram of worms, having a dissociation constant of roughly 1 x 10+E-8 M. In agreement with Stretton's original finding, the drug dissociates very slowly from its bound state (half life ~10 min.). The formation of the bound state also occurs relatively slowly. The rate constant is ~1 x 10+E5 liter/mole-sec at 0 C, several orders of magnitude slower than diffusion-limited binding, implying that a rate-limiting step such as a protein conformational change might be involved with the formation of the bound state observed in vitro. We have screened extracts of several levamisole-resistant mutants having little or no response to the drug as living worms. lev-1(x21) has normal binding activity while unc-74(x19) and unc-29(x29) have none. Several other mutants, unc-38(x20), ), and unc-29(e1O72) apparently have activity altered in amount or affinity. Anyway, all this is a definite first of some sort. We'll try to figure out what and let you know more at the Worm Meeting.