DISULFIDE-LINKED DIMERS OF APOLIPOPROTEIN-D IN URINE

Apolipoprotein (apo) D is a glycoprotein that contains at least one fr ee cysteine. This allows the formation of disulfide linked dimers of a poD, a phenomenon that could interfere with the study of the isoforms of apoD. Consequently, it is important to consider the effects of hete ro- and homodimer formation on the molecular heterogeneity of apoD as well as on the evaluation of the specificity of antibodies to this gly coprotein. The identification of apoD in urine has provided a potentia l new marker of tubular proteinuria [1]. Thus, we have studied the spe cificity of our polyclonal antibodies to apoD against the proteins pre sent in normal urine, and at the same time, the existence of dimeric s pecies of apoD linked by disulfide bonds in urine. The specimens were obtained from apparently healthy individuals and analyzed by Western b lot. The results showed that apoD in urine exists as a mixture of mono mers and dimers, the latter having apparent molecular weights differen t from those occurring in plasma. Only monomeric apoD was observed und er reducing conditions, proving the monospecificity of the polyclonal apoD antibodies.