Heterogeneity of urinary albumin from diabetic patients.

A fundamental cause of diabetic microalbuminuria, heterogeneity of normal and diabetic urinary albumin was shown by affinity chromatography on Cibacron Blue F3GA. By changing the properties of interaction with the matrix, the protein was separated into six fractions. Samples of urinary albumin from proteinuria patients showed the same elution profiles as those of serum albumin, whereas those from controls or normoalbuminuria diabetic patients exhibited different elution patterns. The relative percentage of the resin unbound fraction of urinary albumin was ten or more times higher than that of serum albumin, and the ratio decreased with increasing albumin excretion into urine. More than 6 mol fatty acid/mol albumin combined with the unbound fraction. It is suggested that microalbumin excretion into urine is the result of excessive unesterified fatty acid binding to the protein.