Rat α1-fetoprotein (α1F) has been isolated from amniotic fluid by isoelectric focusing. Rat amniotic fluid was also fractionated by salting out, ion-exchange chromatography, preparative electrophoresis, and molecular filtration. Four major proteins were tentatively identified in amniotic fluid: albumin, transferrin, γG-globulin, and α1F. Rat α1F has a pI of 4.9 and a molecular weight of 70,000. It is difficult to separate from albumin, which has a molecular weight of 60,000 and a pI of 5.6, but immunochemically pure α1F was obtained by two successive isoelectric focusing fractionations. Rabbit antisera to rat α1F does not react with human α1F. α1F is also present in fetal rat sera and pregnant rat sera after 15 days of gestation and in neonatal rat sera until 2 weeks of age. α1F is found in the sera of some rats with transplantable hepatomas, but not in all. This inconsistency is most likely due to the limited sensitivity of the test systems used. Isolation of α1F is necessary to develop a specific, sensitive immunoassay that can be used to measure α1F in experimental models of hepatoma development in rats.

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Supported by Grant CA-12473 from the National Cancer Institute, NIH, Bethesda, Md.

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