Makromolekulare Polysaccharid-Proteine, I. Chondroitinsulfat-Protein aus Rindernasenknorpel — Beziehungen zwischen makromolekularen Eigenschaften und Funktion

Abstract

Complexes of chondroitin sulfate with protein (CS-proteins) were obtained from bovine nasal cartilage by ultracentrifugation, gel filtration and purifica- tion via their cetyl pyridinium complexes. The isolated CS-proteins contain chrondroitin-4-sulfate as the polysaccharide component, and 12-18% of protein which is free from hydraxyproline. Light scattering measurements under defined conditions give a molecular weight (Mw) of about 3 x 106)** for CS-protein from bovine nasal cartilage. This value represents the smallest macromolecular unit, in which 24-32 CS-chains were bound to the protein. Calculations showed that the molecule was rodshaped with a length of about 3000 A, and a radius of gyration RG of 850-1350 A. The CS-protein preparations under investigation were polydisperse (Mw/Mn = 2:1-5:1). After exhaustive degradation of the CS-protein with hyaluronidase, whereby 75% of the carbohydrate (= 60% of the whole molecule) was removed, the molecular weight was 7 x 105. The decrease in molecular weight corresponded to the loss of carbohydrate. In electrolyte solutions, CS-protein showed a strong tendency to form molecular aggregates. In 0.2M NaCl-solution, the apparent molecular weights increase up to 30 x 106; at the same time there was an increase in density, decrease in viscosity and hydration, and conversion of the rod form into a spherical form. From the calculated dimensions of the molecular aggregates with high apparent molecular weights, it seems likely that the individual molecules can associate both side by side and end to end. High NaCl concentrations (1.0[image]) cause the apparent molecular weight to decrease again, with a further increase in density and a decrease again, with a further increase in density and a decrease in viscosity. Measurements at different concentrations of hydrogen ions show that the apparent molecular weight increases up to 5-7 x 107, with an increase in viscosity, as the pH was increased from 4 to 8. The rate of diffusion of glucose was decreased by CS-protein solutions. This retarding effect on diffusion depended on the concentration oi the CS-protein and on the hydrodynamic properties of the CS-protein molecule. The maximal retardation of diffusion was observed at a critical concentration of CS-protein (15-20 mg/ml/) in distilled water (low average particle density). Increasing concentrations of NaCl cause a small retardation of diffusion with a concomitant decrease in the effective number of particles (aggregation of CS-protein molecules). The diffusion of glucose in solutions of CS-protein was inhibited more strongly under weakly acidic or alkaline conditions than at pH 7. The physical (apparent) molecular weight (particle number) and the average particle density were the parameters that determine the degree of retardation of diffusion at the critical concentration of dissolved CS-protein. Since the properties of CS-protein solutions which influence diffusion were affected by slight changes in the solvent, the process of diffusion and transport in the extracellular space can also be controlled under physiological conditions by slight changes in the concentrations of electrolytes or H ions.