[
Worm Breeder's Gazette,
1979]
To compare enzymatic activities of Bergerac and Bristol strains of C. elegans, we used the microsystem ' Api Zym ' focused by D. Monget ( 1978) and produced by the french firm API SYSTEM. Some of these tests, not yet commercialized, were a gift of API SYSTEM. The technique consists in microdishes which are impregnated with substrate and buffer ( PH is given in the table ). We introduced 0.1 ml of biological suspension ( a known number of adult worms sonicated in buffer and resuspended in distilled water after homogenization ) in the microdishes which were incubated at 37 C for 4 hours. Bacteria were grossly eliminated by washing; Afterwards their concentration was too low to give response with Api Zym. The reactions were revealed colorimetrically by 4 /oo ' Fast blue BB '. The intensity of the reaction is proportional to enzymatic activity and is noted from - to +++++ . A reaction noted +/- refers to a low but detectable response. To give reliable results, all the tests were read by the same experimenter and enzymatic activities in Bergerac and Bristol strains were performed at the same time. To date, the tests were carried out on 64 enzymatic activities. Most of the enzymes tested were hydrolases ( phosphatases,esterases, aminopeptidases, glycosidases, arylsulfatases ) and some were dehydrogenases. Some of the enzymatic activities tested seem to take a prominent part in postembryonic development. It's the case of Leucine arylamidase, which plays an important part in molting ( Rogers 1965, 1977 ), and could be also the case of glycyl-L-proline arylamidase which is implicated in the metabolism of collagen. The results are summarized in the following table. The two strains show similar enzymatic spectra, but differences can be noted, which are localized essentially on : - Trypsin ( n 8 ) - gamma L-glutamate transpeptidase ( n 38 ) - Glycyl-glycine arylamidase ( n 42 ) - L-threonine arylamidase ( n 54 ) - N-CBZ-glycyl-glycyl-L-arginine arylamidase ( n 56 ) Other differences, in a less degree, but yet detectable, are observed on: - Alkaline Phosphatase ( n 1 ) - L-histidine arylamidase ( n 33 ) - L-leucyl-glycine arylamidase ( n 45 ) - L-ornithine arylamidase ( n 51 ) - L-serine arylamidase ( n 53 ) All the differences observed in this table have been verified in two repetitions, which have similar results. But it could be argued that these differences could be due to nutritional adaptation, because these two strains, xenically cultured on the A1 medium ( for thirty years in case of Bergerac, and one year in the case of Bristol ) are associated with a different bacterial complex. [See Figure 1]
[
Worm Breeder's Gazette,
1990]
We have been studying C. elegans microtubules from cellular and genetic aspects. Since scanning tunneling microscopy (STM) can provide atomic resolution of metals and semiconductive surfaces; our objective is to obtain images of C. elegans microtubules resolved at the atomic level. However, application of STM to biomolecules is faced with a variety of problems, including poor electrical conductivity, flexible stability under STM imaging conditions. In spite of limitations, recently, impressive images of DNA biomolecules have been obtained at atomic resolution. Microtubules (MT) were isolated from 30g of freshly grown N2 worms according to the procedure of Aamdot and Culotti 1986, and Siddiqui et al 1989, using cycles of temperature dependent assembly and disassembly (Shelanski, et al. 1973). Assembled MT were taken in MT isolation buffer (containing 0.1mM GTP, 20 M taxol, and 2.0 mM DTE), diluted tenfold and fixed in glutaraldehyde (0.1%). The samples were kept frozen at -20 C, for 4-5 days. The STM imaging samples were thawed, and a drop was smeared onto a chip of freshly cleaved HOPG ( highly oriented pyrolitic graphite, Union Carbide), and allowed to air dry at room temperature. The STM images were obtained using 'Nanascope II Digital Instruments, California (Sam Howell and C. Lee, kindly helped with the STM settings). All STM imaging was conducted at atmospheric pressure and at room temperature (22 C). Two different STM images of C. elegans MT are shown here. [See Figure 1] Most of our STM scans of MT correspond to one or two microtubules, but they appear flattened and bent along the seams of the protofilaments. The dimensions of alpha and -tubulin dimer subunits are about 8 nm, and each protofilament has a width of 4.6 nm. The flattening and buckeling of protofilaments along the seams could arise due to the fixation conditions, or caused by the STM current flow through the specimen. At present, we are unable to attribute this observation to any single factor, and the images of MT do not provide any higher resolution than conventional electron microscopy using negative staining. But it is increasingly possible that one may be able to resolve individual amino acids or even atoms using STM. We plan to continue looking for improved conditions for better STM or AFM images of C. elegans MT. Brief description of STM: Scanning tunneling microscopy (STM) traces three dimensional images of surfaces - even at the level of individual atoms. Gerd Binnig & Heinrich Rohrer of IBM Zurich received the Nobel Prize in 1986 for STM (Refer, e.g.: Scientific American, August,1985). Briefly in STM, the 'aperture' is a small tungston probe, its tip extremely fine (about 0. 2 nm in width, and may consist of a single atom). Piezoelectric controls move the tip within a nanometer or two of the surface of the conducting sample, allowing an overlap between the electron clouds of the atom at the probe tip and the closest atom of the sample placed on the surface. As a small voltage is applied to the tip, electrons 'tunnel' across this gap, creating a tiny tunneling current. The strength of the tunneling current is exponentially sensitive to the width of the gap (about an order of magnitude per angstrom). Depending on the substrate, typical currents and voltages are in the range of nanoamperes and millivolts. A servo system uses a feedback control that keeps the tip to substrate gap constant, by modulating the voltage across a piezoelectric positioning system (Piezoceramic materials expand or shrink extremely small distances (i.e. angstroms ) in response to the applied voltage. As the tip scans the surface, variations in this voltage, when plotted correspond to surface structure. I wish to thank members of Ward lab (Alicia, Andrea, Bill, Bonnie, Bruce, Jacob, John and Paul); Hameroff Lab (Dolly, Larry, Mohammad, and Richard); and Sarid Lab (Sam and Lee).