Characterization of soluble forms of NCAM

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Abstract
Neural cell adhesion molecule (NCAM) has been described as a family of membrane glycoproteins. However, soluble NCAM immunoreactivity has long been recognized. We here show that soluble NCAM is composed of two quantitatively major polypeptides of M r 180 000 and 115 000 and two minor components of M r 160 000 and 145 000. Soluble NCAM was immunochemically identical to membrane NCAM, was polysialylated and carried the HNK‐1 epitope. It only constituted 0.8% of total NCAM in newborn rat brain. Soluble NCAM appeared in neuronal cell culture medium 15–30 min after the start of synthesis preceding accumulation of membrane‐associated NCAM on the cell surface. This indicates that soluble NCAM contains a secreted component.