Five complexes consisting of one acidic and one basic subunit that were linked via disulfide bonds were purified from unreduced S-alkylated glycinin. The acidic and basic subunits were identified unambiguously using NH2-terminal sequence analysis, sodium dodecyl sulfate (SDS)-electrophoresis, and analytical isoelectric focusing. The subunit pairings are A1aB2, A1bB1b, A2B1a, A3B4, and F2(2)B3. Polypeptide A4 was not linked to a corresponding basic subunit via a disulfide bond. The study shows that pairing between subunits is nonrandom, which is consistent with evidence that glycinin is synthesized as a Mr = 60,000 precursor that undergoes post-translational modification to form the individual linked subunits.