A sulfated glycoprotein was isolated from the culture media of Drosophila Kc 
cells and named papilin. Affinity purified antibodies against this protein 
localized it primarily to the basement membranes of embryos. The antibodies 
cross-reacted with another material which was not sulfated and appeared to be 
the core protein of papilin, which is proteoglycan-like. After reduction, 
papilin electrophoresed in sodium dodecyl sulfate-polyacrylamide gel 
electrophoresis as a broad band of about 900,000 apparent molecular weight and 
the core protein as a narrow band of approximately 400,000. The core protein was 
formed by some cell lines and by other cells on incubation with 1 mM 
4-methylumbelliferyl xyloside, which inhibited formation of the 
proteoglycan-like form. The buoyant density of papilin in CsCl/4 M guanidine 
hydrochloride is 1.4 g/ml, that of the core protein is much less. Papilin forms 
oligomers linked by disulfide bridges, as shown by sodium dodecyl 
sulfate-agarose gel electrophoresis and electron microscopy. The protomer is a 
225 +/- 15-nm thread which is disulfide-linked into a loop with fine, protruding 
thread ends. Oligomers form clover-leaf-like structures. The protein contains 
22% combined serine and threonine residues and 25% combined aspartic and 
glutamic residues. 10 g of polypeptide has attached 6.4 g of glucosamine, 3.1 g 
of galactosamine, 6.1 g of uronic acid, and 2.7 g of neutral sugars. There are 
about 80 O-linked carbohydrate chains/core protein molecule. Sulfate is attached 
to these chains. The O-linkage is through an unidentified neutral sugar. Papilin 
is largely resistant to common glycosidases and several proteases. The degree of 
sulfation varies with the sulfate concentration of the incubation medium. This 
proteoglycan-like glycoprotein differs substantially from corresponding 
proteoglycans found in vertebrate basement membranes, in contrast to Drosophila 
basement membrane laminin and collagen IV which have been conserved 
evolutionarily.