Human α‐L‐iduronidase: 1. Purification, monoclonal antibody production, native and subunit molecular mass

Human α‐L iduronidase from liver was purified about 20 000‐fold with a new rapid three‐step, five‐column procedure which consisted of a Concanavalin‐A–Sepharose/Blue‐A–Agarose coupled step, a CM‐Sepharose/Bio‐Gel HT coupled step followedby a cupric‐ion‐chelating Sepharose 6B step. The behaviour of α‐L‐iduronidase on gel permeation chromatography was dependent upon both pH and ionic strength of the eluting buffer. The formation of species with enzyme activity which behaved as large‐molecular‐mass aggregates was favoured under conditions of low ionic strength and neutral pH. The amount of high‐M_r species diminished as the pH decreased or the ionic strength increased to favour a single active species of M_r 65000. A specific monoclonal antibody was generated against liver α‐L‐iduronidase. The antibody specifically immunoprecipitated enzyme activity from both crude and purified sources. The subunit M_r of liver α‐L‐iduronidase was estimated to be 65000 using SDS‐PAGE. Monoclonal antibody immunoprecipitation of radiolabelled enzyme was used to provide definitive confirmation of this subunit size.