Accessibility of sialo components in a murine tumor cell to extracellular N-acetylneuraminate glycohydrolase (sialidase).

Lipid-bound sialic acid in the murine melanoma cell is not totally inaccessible to an exogenous macromolecular probe, as formerly believed. Roughly 30% of the dialic acid bound to lipid, and an equal proportion of the sialic acid bound to protein is cleaved by the action of Clostridium perfringens N-acetylneuraminate glycohydrolase (neuraminidase, sialidase) when the purified enzyme is added to the suspenion medium of intact murine melanoma cells freshly derived from the tumor. Cleavage of lipid-bound sialic acid is indifferent to the presence of Ca (2+) in the medium. However, maximum release from protein requires a physiological concentration of this divalent cation. Variation in ionic strength has no effect on release of sialic acid. These findings show that restricted portion of the bound sialic acid may be released from the intact murine melanama cell by the extracellularly supplied enzyme acting topographically.