In vitro studies on ³⁵S‐sulfate incorporation into the acid mucopolysaccharides of chick embryo cardiac jelly

An experimental model has been devised for the study of radioactive sulfate incorporation into the cardiac jelly of the isolated stage 18–19 (three‐day) chick embryo heart. Isotope incorporation was found to be optimal in an incubation medium containing glucose, but containing no added unlabeled sulfate. The rate of isotope uptake demonstrated a slight lag during the first 5 to 10 minutes followed by a linear incorporation of at least four hours duration. It is believed that 35 S‐sulfate incorporation into the hearts reflects sulfated acid mucopolysaccharide synthesis, and that this system will therefore be useful in studying the significance of this group of compounds in the cardiac jelly. Radioactive sulfate incorporation per unit weight has been found to be inversely proportional to heart weight (i.e., embryo age) over the span of development from stage 14 to stage 24. This probably reflects the fact that cardiac jelly makes up proportionately a greater part of the younger hearts. Sodium salicylate has been shown to inhibit 35 S‐sulfate incorporation in this system, in direct relation to its concentration in the incubation medium. This is given as one example of the type of investigation to which this system is adaptable.