Role of sialic acid in exogenous protein accumulation and water retention by the egg jelly of the salamander Ambystoma macrodactylum

The jelly coat of eggs from the salamander Ambystoma macrodactylum is capable of binding and accumulating a high concentration of exogenous protein from a dilute incubation medium. This binding appears to be due to negatively charged moeities of the jelly structure. To examine whether sialic acid was responsible for the binding of exogenous protein as well as water retention, and thus the structural rigidity of the jelly, sialic acid was chemically removed from the jelly. There appeared to be a linear relationship between the sialic acid content of the jelly and the amounts of exogenous protein and water retained by the jelly. Furthermore, removal of about 90% of the sialic acid was associated with 89% and 70% decreases in accumulated hemoglobin and water content, respectively. The data are therefore consistent with the hypothesis that sialic acid is the exogenous protein binding site. The data are also consistent with the hypothesis that sialic acid is responsible for most of the water retention and thus the swollen state of the egg jelly.