High performance ion exchange chromatography of human plasma lecithin:cholesterol acyltransferase

Highly purified monomeric human plasma lecithin:cholesterol acyltransferase (LCAT), completely free of apolipoprotein D, has been chromatographed on a MonoQ HR 5/5 anion exchanger. LCAT eluted as symmetrical peaks after 12.8 min and 14.8 min at pH 5.0 and pH 6.0, respectively, using a linear NaCl gradient. The corresponding concentrations of NaCl effecting desorption of LCAT from the anion exchanger were 125 mM and 175 mM. At both pH values human serum albumin eluted earlier and was well separated from the enzyme. Rechromatography of LCAT in the eluates from these experiments at acid pH, on high performance gel filtration, demonstrated absence of aggregation. The nonspecific adsorption during anion exchange chromatography at pH 5.0 and pH 6.0 was negligible, as demonstrated by a linear relationship between injected amounts of LCAT and recorded peak areas for a 2-20 micrograms protein range. Zone immunoelectrophoresis assay indicated unaltered immunoreactivity of the eluted LCAT.