ABSTRACTr Circular dichroic spectra of camel fl-endorphin and ovine f3-lipotropin in water show little, if any, secondary structure. Intrinsic viscosities and sedimentation coefficients of the two peptides also suggest that the molecules are not compact and globular. Methanol or sodium dodecyl sulfate promotes the formation of helical structure to an extent as much as one-half of either peptide molecule. The The presence of an endogenous ligand for the opiate receptor found in brain tissue has been demonstrated by Terenius, Snyder, Simon, and their coworkers (1-3), using a modification of a method suggested by Goldstein et al. (4). Two pentapeptides with opiate-like activity (Met-enkephalin, H-Tyr-GlyGly-Phe-Met-OH, and Leu-enkephalin, H-Tyr-Gly-Gly-PheLeu-OH) were isolated from pig brains by Hughes et al. (5). A polypeptide with potent opiate-like activity was isolated from camel pituitary glands by Li and Chung (6), and its amino acid sequence, identical to the COOH-terminal 31 amino acid residues of sheep /3-lipotropin (7-9), was determined (6). This peptide was designated /3-endorphin. The enkephalins (5) are related to the first five NH2-terminal residues of /3-endorphin (6). Both camel and human endorphins have been synthesized (10,11). Their sequences (6, 12) differ in only two positions (see Fig. 1). These two molecules are equipotent in both in vitro (12) and in vivo (11) bioassays for opiate-like activity.The conformations of the enkephalins, /3-endorphin, and /3-lipotropin have been investigated by several groups. Proton magnetic resonance studies have suggested that Met-enkephalin exists as a single (-turn in fully deuterated dimethyl sulfoxide (13-16), while circular dichroism (CD) studies indicate that the addition of salt to aqueous solutions of Met-enkephalin induces a "/3-like" structure (17). Little is known about the conformations of the (3-endorphins, although two preliminary reports have indicated that these molecules are low in helical content in water, but become more helical in trifluoroethanol (18,19).Similarly, /3-lipotropin is reported to contain about 12% a-helix in dilute salt solutions, which increases to 30% in 50% dioxane/water (20). The ability of nonpolar solvents to produce helical structures in /3-lipotropin has also been observed by We report here on the conformations of human /3-endorphin (/3h-endorphin) and camel /3-endorphin (/3c-endorphin) and sheep /3-lipotropin (/3,-lipotropin) in water, methanol, and sodium dodecyl sulfate (NaDodSO4) solutions as determined by CD and hydrodynamic studies. In addition, the limitations ofThe costs of publication of this article were defrayed in part by the payment of page charges from funds made available to support the research which is the subject of the article. This article must therefore be hereby marked "advertisement" in accordance with 18 U. S. C. §1734 solely to indicate this fact. 3235predicting the secondary structure of these types of molecules from their primary structure, and of interpreting their CD spectra in terms of s...

Thrombin has been shown to resynthesize the Argl34-Thrl"s peptide bond between the 134-and 57-residue thrombin fragments of reduced and carbamidomethylated human somatotropin at pH 6.0 in 90% (voVvol) glycerol. The maximal amount ofsynthesis was about 20% as estimated by sodium dodecyl sulfate gel electrophoresis and radioreceptor assay. The resynthesized polypeptide was isolated and shown to be indistinguishable from the reduced and carbamidomethylated hormone when tested by two receptor-binding assays, radioimmunoassay, and rat tibia test.