Worm Breeder's Gazette 2(1): 9
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.
An exhaustive extraction procedure has been used to extend our previous studies on C. elegans cholinesterase. A total of four separable forms of cholinesterase have been identified. They are form I (5.3 + 0.3S), form II (7.1 + 0.4S), form III (11.4 + 0.5S) and form IV (13.0 + 0.6S). Repeated extraction of homogenate pellets with 0.05 M, pH 8. borate buffer removes all of the predominant form I and most of the less frequent form IV. Small amounts of forms II and III are also removed, but most of these forms remain in the pellet and require detergent for extraction. After detergent extraction no detectable activity remains in the pellet. The four separated forms have been examined by Km's, substrate specificities, inhibitor specificities, and sensitivities to thermal and detergent inactivation. In all these respects the four forms fall into two classes: A (forms I and II) and B (forms III and IV). The A forms have 4-fold higher Km's, have somewhat higher preference for acetyl- (as opposed to other acyl-) thiocholine substrates, are generally less sensitive to inhibition, and are considerably more sensitive to thermal and detergent inactivation. The differences between these forms, although clear and unmistakable, are sufficiently small to make it unclear whether the two classes share a common active-site-containing subunit. Using the established differences in detergent sensitivity between C. elegans cholinesterases of the A and B types, a procedure has been designed to screen available mutants for possible differences in the amounts and/or properties of these two types. Among 89 mutants examined, one ( BC46) was detectably different from wild type, and turned out upon further examination to be completely deficient in the B type cholinesterase forms (III and IV). Both A forms (I and II) remain in the mutant and are not detectably altered from wild type. The mutant grows and reproduces at normal rates, but is uncoordinated; head movements appear relatively normal, but waves of con- traction usually fail to propagate backward into the body. Sensory responses to mechanical, chemical and osmotic stimuli can be demonstrated. After several backcrosses to wild type, the behavioral and biochemical defects have not been separated, and both map to the X-chromosome. Further work is in progress to examine two implications of these results: (l) that forms III and IV may be encoded by a separate structural gene, and (2) that forms III and IV may have a discrete and functionally-related distribution in the animal.