CIRCULAR-DICHROISM OF MAMMALIAN FOLLITROPINS AND EFFECTS OF TREATMENT WITH N-BROMOSUCCINIMIDE

The circular dichroism of the tryptophan containing glycoprotein hormone, follitropin, displays bands in the near ultraviolet which are absent in homologous, tryptophan-free hormones. In the far ultraviolet, the dichroism is very similar to the other glycoprotein hormones with little or no indication of α-helix. The single tryptophan of follitropin is in a domain of the β subunit sequences of these hormones which is highly conserved from hormone to hormone. Without prior dissociation of the follitropin into subunits, no change is seen in circular dichroism, absorption at 280 nm, fluorescence emission or hormonal activity after treatment with N-bromosuccinimide. In contrast, these properties change when intact human lutropin is studied; its tryptophan residue is a position different than in follitropin. These results support the proposal that the domain containing the tryptophan in follitropin is in or near a region of subunit-subunit contact in the glycoprotein hormones. © 1978.