The Molecular Properties of ApoA-I from Human High Density Lipoprotein

Abstract

Abstract The molecular properties of the principal protein component of human high density lipoprotein have been evaluated in aqueous solution at pH 2.0, 7.4, and 12.0 and in guanidine hydrochloride at pH 7.4. The high helical content observed at neutral pH by circular dichroism is partly eliminated in acid, more extensively lost in alkali, and almost completely lost in 1.7 m guanidine hydrochloride. The fluorescence properties of the tryptophanyl residues also indicate greater loss of structure in 1.7 m guanidine hydrochloride than in aqueous solutions at any pH. ApoA-I contains both secondary and tertiary structure in water at neutral pH comparable to that found in native globular proteins and undergoes molecular transitions below pH ∼7, above pH ∼11, and in guanidine hydrochloride solutions between 0.8 to 1.4 m. The properties of succinylated apoA-I at neutral pH resemble those of apoA-I at pH 12.0.