Fetal and adult albumins are indistinguishable by immunological and physicochemical criteria

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Abstract
The existence of a functionally immature fetal albumin was postulated to explain the reduced ability of newborn plasma to bind bilirubin and various drugs. Cord and adult albumin, isolated by a simple salting-out technique, were reported to differ in electrophoretic and chromatographic properties and in their resistance to alkali and proteolytic enzymes. The interpretation of these findings has since been questioned. To resolve this controversy, human serum albumins from pooled umbilical cord and adult donor plasma were purified to homogeneity. The 2 albumins were compared and were indistinguishable by polyacrylamide gel electrophoresis with and without sodium dodecyl sulfate, as well as by immunoelectrophoresis and double immunodiffusion using specific antibodies against both albumins. The amino acid compositions, the amino-terminal sequence Asp-Ala-His-Lys-Ser-Glu-Val-Ala-, the carboxy terminus Leu, and the peptide fingerprints were identical in the 2 albumins. No significant differences were found by circular dichroism in the UV 200-350 nm. Binding studies with bilirubin showed association constants of 3.7 .+-. 0.7 .times. 107 M-1 for cord and 2.9 .+-. 0.3 .times. 107 M-1 for adult albumin, respectively. The circular dichroic spectra of 1:1 bilirubin.cntdot.albumin complexes showed considerable variation between the batches but were not significantly different. The only difference was found in the fluorescence spectra of the bilirubin.cntdot.albumin complexes, where complexes with adult albumin showed only 75% of the relative fluorescence exhibited with cord albumin. The combined results nevertheless strongly indicate that fetal and adult albumins are very similar, if not identical.