A new efficient technology for the isolation of human alpha-fetoprotein and the status of free sulfhydryl and amino groups in the resulting preparation

A new preparative method for the isolation of human alpha -fetoprotein (AFP ) from cord blood serum was described. This involves the precipitation of h igh-molecular compounds with polyethylene glycol and affinity, ion exchange , and gel permeation chromatographies. Up to several tens of milligrams of the homogeneous AFP can be rapidly (48 h) prepared in a high yield per one isolation cycle. The native structure of the isolated AFP was proved by imm unochemical analysis. No free sulfhydryl groups were found in the purified AFP, and its reduction with dithiothreitol at 4 degreesC led to the formati on of two sulfhydryl groups probably belonging to the Cys18 and Cys67 resid ues in domain I of the protein molecule. Up to ten amino groups in the puri fied AFP were shown to be accessible to a mild modification by 3-(2-pyridyl dithio)propionic acid N-succinimide ester.