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Glycoproteins are present in the web of the orb-weaving spiders Argiope trifasciata and Argiope aurantia. Periodic acid-Schriff reactive glyco-proteins are confined in large part, to the sticky spiral and sticky spiral-radial junctions. Glycoproteins containing amino sugars appear associated with all fibers, especially the radial fibers. Enzymes may be used to remove glycoproteins selectively from the sticky spiral and stabilimentum.

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The digestive fluid of Argiope was assayed for its proteolytic activity with selected natural and synthetic substrates.1. Peak proteolytic activity was observed a t pH 7.8. This was coincident with the pH of the digestive fluid.2. Elastolytic and weak chymotryptic activities were detected. Limited activity toward collagen was also observed. Activity toward substrates for trypsin, leucine aminopeptidase and carpboxypeptidase A and B was absent.3. Evidence demonstrating the in vitro digestion of web fibroin was obtained. The viscid spiral was susceptible to a variety of proteases; the radial fibers to the spider enzyme alone.4. Of a series of inhibitors studied, EDTA had the greatest effect upon the spider proteases. This effect was temperature dependent.There is a growing body of information on the digestive proteases of invertebrates. The introduction of synthetic substrates and inhibitors now allows additional criteria for comparing the phylogenetic relationship between these and the vertebrate proteases (Neurath et al., '67; Barnard, '73).To our knowledge the most recent study on the digestive enzymes of spiders is that of Pickford ('42). She observed considerable proteolytic activity in both tissue extracts and gut fluids at alkaline pH values. In the present study we have sought to identify the specific catalytic nature of these proteases.Breed et al. (' 64) and Peakall ('72) have presented evidence, based on radioactive tracer studies, that orb-weaving spiders are capable of digesting their own web. The present study examines the effect of the digestive fluids on the orb-web fibroin. MATERIALS AND METHODSMature female Argiope were collected locally and identified by the criteria of Kaston ('52) as A. aurentia. Each spider was held gently with a cotton swab while fluid expressed from its mouth parts was collected in a 2O-pl pipette. The fluid was stored at -20°C until studied. The extent to which venom contributed to the fluid so expressed has yet to be evaluated. J. EXP. ZOOL.. 202: 213-222. Thermal stabilitySpider digestive fluid was diluted to a protein concentration of 0.5 mg/ml in 0.05 M borate buffer, pH 7.8 and pre-equilibrated at a temperature selected between 15" to 70°C at 5" intervals. The dilute enzyme mixture was then maintained at the selected temperature for 20 minutes before being rapidly brought to 25°C for assay with casein as described below. Enzyme assaysGeneral protease activity was assayed by a modified method of Kunitz ('47). The reaction mixture consisted of 2.5 ml 1% Hammarsten casein (Sigma Chemical Co.) in 0.05 M borate-KC1-NaOH buffer, pH 7.8 and 0.3 ml of distilled water. After equilibration for ten minutes a t 37"C, the reaction was initiated by the addition of 0.2 ml of diluted enzyme and allowed to incubate for 30 minutes. The reaction was terminated by the addition of 4.0 mi 5% trichloroacetic acid (TCA) and set aside for one hour. The precipitate was removed by filtration and the absorbance of the supernatant at O.D.zso was measured. Blank values were obtained by add...

The minimum number of secretion products used by the spiders Araneus trifolium and Argiope trifasciata to construct their orb webs has been established by selective enzyme digestion and histochemical staining, as well as differential isotope localization in these webs. Three fiber types are present in the webs: (a) a major fiber found throughout the web, (b) a minor fiber found only in radial threads, and (c) the core fibers of the sticky spiral thread. Three nonfibrous secretions are found on these fibers. These include a water soluble viscid coating of the sticky spiral and two adhesives which fasten the threads of the web together; one found only at junctions of sticky spiral and radial threads and the other at all other thread connections. The possible glandular sources of these secretions are discussed.