Microheterogeneity of human placental lactogen showing different patterns in individuals

Samples of human placental lactogen, obtained either as a standard pooled preparation or prepared from individual placentas, were shown to migrate as a single band on acrylamide gel electrophoresis. When subjected to isoelectric focusing in polyacrylamide gels, the pooled sample was resolved into bands at pI values 5.0, 5.5, 5.8. 6.0, 6.1 and 6.2. Different batches of the standard pooled sample gave different proportions of each isoprotein species. Isolation and refocusing of individual bands did not alter the pI of each. Treatment with urea or with p-chloromercuribenzoate did not eliminate microheterogeneity seen on isofucising, indicating that the observed heterogeneity is probably not due to conformational differences or to restriction of molecular shape of disulfide bonds. It was shown by immunodiffusion that all the isofocusing reacted similarly against a common antibody to human placental lactogen. When placental lactogen was extracted from individual full term human placentas, the same isoprotein bands were observed but their proportions varied markedly from one placenta to another, and not all bands were present. Thus human placental lactogen displays considerable microheterogeneity which varies with individual placentas.