Neurite-promoting activity from fetal skeletal muscle: Immunological comparison with laminin

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Abstract
Polycation‐binding neurite‐promoting factor (PNPF) from skeletal muscle of bovine fetuses has been compared to mouse tumor laminin by an immunological approach. Antiserum prepared against PNPF blocked the neurite‐promoting activity in a dose‐dependent manner. The anti‐PNPF antiserum bound to Mr = 200,000‐;195,000 bands as well as several components of higher molecular weight, as detected in immunoblots of reduced PNPF. The anti‐PNPF antiserum did not inhibit the neurite‐promoting activity of mouse laminin, although it did bind to native laminin. Antilaminin antiserum bound to PNFP and identified the same Mr = 200,000−195,000 bands and two other higher‐molecular‐weight bands, as did the anti‐PNPF antiserum. The activity of PNPF was confirmed to be sensitive to treatment with heparitinase. It is concluded that PNPF from bovine fetal muscle contains a complex of heparan sulfate and high‐molecular‐weight components, particularly of Mr = 200,000‐195,000, which share antigenic determinants with mouse laminin. However antilaminin antiserum fails to inhibit the activity of PNPF, suggesting that the active site, and/or adjacent regions, of PNPF are antigenically different from the neurite‐promoting site of purified mouse tumor laminin.