Chondroitin sulfate changes in puppy rib cartilage during the period of calcification

Abstract

Using a single litter of seven puppies, it was found that in the period (13–30 weeks of age) when calcification was occurring in most of the ribs there was a change in the extractability of the chondroitin sulfate in this tissue. There was a decrease in the amount of chondroitin sulfate which could be extracted by homogenizing with water and an increase in the amount which was extracted subsequently by homogenization with alkali. This change was not due to binding of chondroitin sulfate to solid mineral matter because it was found also in a single uncalcified rib from an older puppy in which all but the first two anterior ribs were heavily calcified. It was also found when EDTA was used to extract the solid mineral matter. Measurement of specific activities after injection of radioactive sulfate showed that there was little change in the relative rates of synthesis of the water-soluble and water-insoluble chondroitin sulfate fractions as the age of the puppies increased. This leaves a change in the relationship of protein to chondroitin sulfate in complexes of the two as the most likely explanation for the observed change in extractability.