Age-related changes in chemical composition and physical properties of mucus glycoproteins from rat small intestine

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Abstract
Mucus glycoproteins from newborn and adult rat small intestine were radiolabeled in vivo with Na235SO4 and isolated from mucosal homogenates by using Sepharose 4B column chromatography followed by CsCl-density-gradient centrifugation. Noncovalently bound proteins, lipids and nucleic acids were not detected in the purified glycoproteins. Amino acid, carbohydrate and sulfate compositions were similar to chemical compositions reported for other intestinal mucus glycoproteins, as were sedimentation properties. There were, however, important differences in the chemical and physical characteristics of the mucus glycoproteins from newborn and adult animals. The buoyant density in CsCl was higher for the glycoproteins from newborn rats (1.55 g/ml vs. 1.47 g/ml). On sodium dodecyl sulfate/polyacrylamide per agarose-gel electrophoresis, the glycoprotein from newborn rats had a greater mobility than the adult rat sample. Although both preparations had similar general amino acid compositions, variations were observed for individual amino acids. The total protein content was greater in the glycoprotein from newborn animals (27%, wt/wt, vs. 18%, wt/wt). The molar ratio of carbohydrate to protein was less in the newborn, primarily owing to a decreased fucose and N-acetylgalactosamine content. Comparison of the molar ratio of fucose and sialic acid to galactose for both glycoproteins demonstrated a reciprocal relationship similar to that described by Dische. The sulfate content was greater in the glycoprotein from newborn rats (5.5%, wt/wt, vs. 0.9%, wt/wt). Both had similar sedimentation coefficients in a dissociative solvent. An age-related difference in the types of mucus glycoproteins synthesized by small intestine is suggested.