ACIDIC STRUCTURAL PROTEINS OF CONNECTIVE TISSUE .I. SOLUBILIZATION AND PRELIMINARY CHEMICAL CHARACTERIZATION

1. 1. A new class of proteins which was intimately associated with the insoluble matrix was demonstrated in the skin, joint capsula and placenta of rat, rabbit, calf and human. These proteins correspond to 20-40% of the noncollageneous proteins in the whole tissue and were designated acidic structural proteins because of their property to undergo a reversible isoelectric precipitation between pH 3.7 and 5.7. 2. 2. The acidic structural proteins occur in the tissue in two different states of aggregation. The one part could be solubilized by either 8 M urea, 6 M guanidine, 2% sodium dodecyl sulfate or 0.1 M Na2CO3; the other, and in most cases, predominating part could be solubilized only by dilute NaOH or NaBH4. It seems possible that the latter part is covalently cross-linked. After the solubilization the acidic structural proteins are probably denatured and now highly soluble in water. 3. 3. The acidic structural proteins have a carbohydrate content mostly not exceeding 1%. Acidic mucopolysaccharides are virtually absent. The amino acid composition is quite different from those of collagen and elastin and is characterized by about 25 mole% acidic and 35-40 mole% hydrophobic amino acid residues. Significant amounts of tryptophane, but practically no hydroxyproline, were present. © 1969.