Identification and quantification of apolipoprotein D in normal human urine

Apolipoprotein D has been identified in normal human urine, using sodium dodecyl sulfate-polyacrylamide gel electrophoresis, followed by immunoblotting with monospecific antibodies. Urinary apolipoprotein D appeared as a main 33,000 u protein together with a minor fraction corresponding to its partially deglycosylated species of lower molecular mass. No high molecular mass forms of apolipoprotein D naturally occurring in plasma could be detected. The apolipoprotein D mean +/- SD concentration assayed with rocket immunoelectrophoresis, in urine samples from nine apparently healthy normal men, was 1.4 +/- 1.0 mg/L (range: 0.2-3.0 mg/L). Among the plasma apolipoproteins, apolipoprotein D behaves uniquely as regards its excretion in urine; the other apolipoproteins belonging to the A, B, D and E groups, although of low molecular masses, are present, at most, in trace amounts in normal urine.