Hyaluronate‐Binding Proteins of Murine Brain

The distribution of hyaluronate‐binding activity was determined in the soluble and membrane fractions derived from adult mouse brain by sonication in low‐ionic‐strength buffer. Approximately 60% of the total activity was recovered in the soluble fraction and 33% in membrane fractions. In both cases, the hyaluronate‐binding activities were found to be of high affinity ( K D = 10‐ 9 M ), specific for hyaluronate, and glycoprotein in nature. Most of the hyaluronate‐binding activity from the soluble fraction chromatographed in the void volume of Sepharose CL‐4B and CL‐6B. Approximately 50% of this activity was highly negatively charged, eluting from diethylaminoethyl (DEAE)‐cellulose in 0.5 M NaCl, and contained chondroitin sulfate chains. This latter material also reacted with antibodies raised against cartilage link protein and the core protein of cartilage proteoglycan. Thus, the binding and physical characteristics of this hyaluronate‐binding activity are consistent with those of a chondroitin sulfate proteoglycan aggregate similar to that found in cartilage. A 500‐fold purification of this proteoglycan‐like, hyaluronate‐binding material was achieved by wheat germ agglutinin affinity chromatography, molecular sieve chromatography on Sepharose CL‐6B, and ion exchange chromatography on DEAE‐cellulose. Another class of hyaluronate‐binding material (25–50% of that recovered) eluted from DEAE with 0.24 M NaCl; this material had the properties of a complex glycoprotein, did not contain chondroitin sulfate, and did not react with the antibodies against cartilage link protein and proteoglycan. Thus, adult mouse brain contains at least three different forms of hyaluronate‐binding macromolecules. Two of these have properties similar to the link protein and proteoglycan of cartilage proteoglycan aggregates; the third is distinguishable from these entities.