Based on circular dichroism (CD) and the sequence-predictive method, the opioid-binding cell adhesion molecule (OBCAM) consisted of one half beta-sheets and one fourth alpha-helices. This is consistent with significant sequence homology of the protein to several members of the immunoglobulin (Ig) superfamily, particularly cell adhesion molecules, which are rich in beta-sheets. Hydropathy analysis suggests that hydrophobic and hydrophilic regions were evenly distributed along the sequence, but the NH2- and COOH-termini were hydrophobic. Hydrophobic moments and Fourier-transform amphipathic analyses further suggest that residues 23-30 and 83-93 were amphipathic beta-sheets. The overall conformation of OBCAM was unaltered by adding linoleic acid, which is required for opioid ligand binding.