Comparison of Proteoglycans Extracted by Saline and Guanidinium Chloride from Cultured Chick Retinas

To compare the loosely associated sulfated proteoglycans with those tightly bound to membranes, retinas from 14‐day chick embryos were subjected to progressively disruptive techniques. The most easily removed proteoglycans were isolated from the medium in which the tissue was labeled with [ 35 S]sulfate. On the average, 25% of the glycosaminoglycans were in the labeling medium, 39% were in proteoglycans extracted from the tissue in the balanced salt solution, 32% were in a 4 m ‐guanidinium chloride (GuCl) fraction, and 4% remained unextracted. These glycosaminoglycans contained, respectively, 28, 28, 40, and 4% of the incorporated [ 35 S]sulfate. On the basis of electrophoretic mobility and TLC of chondroitinase digests, the ratio of 35 S in chondroitin sulfate to that in heparan sulfate was 4–7 times higher in the medium and balanced salt extracts than in the GuCl extracts. In both extracts there was more 35 S in chondroitin‐6‐sulfate than in chondroitin‐4‐sulfate. Dialysis of the extracts against 0.5 M‐NaCl resulted in the precipitation of about 12% of the glycosaminoglycans in the saline extracts and about 40% in GuCl extract. These subfractions, which were relatively enriched in heparan sulfate, were largely soluble in dithiothreitol in 8 m ‐urea (DTT). Similarities between the proteoglycans in the medium and those extracted by balanced salt solutions suggest that the saline‐extracted proteoglycans were for the most part loosely associated with cell surfaces or extracellular matrices, whereas the GuCl‐extracted proteoglycans probably were bound to membranes.