Biotin as a probe of the surface of Ascaris suum developmental stages.

Sulfo-NHS-biotin (aqueous soluble) and NHS-biotin (organic soluble) labeled similar SDS-2ME (sodium dodecyl sulfate/beta-mercaptoethanol) soluble cuticular proteins of second stage larvae (L2) and third stage Ascaris suum larvae (L3). Comparable analysis of biotin-labeled fourth stage larvae (L4), young adults, and mature adult Ascaris suum revealed strong labeling of several SDS-2ME soluble cuticular proteins with NHS-biotin, while sulfo-NHS-biotin appeared to strongly label a single SDS-2ME soluble cuticular protein. Both biotin probes labeled only cuticular proteins, since no evidence of internal labeling was observed in any developmental stage examined by either electroblot analysis or by electron microscopy. Our data suggest a greater cuticular permeability to the organic soluble biotin reagent in the later developmental stages (greater than L3) of A. suum than to the aqueous soluble biotin reagent, and may indicate the presence of a hydrophobic barrier in the cuticle of the later stages of the parasite.