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The binding of cancer cells to the basement membrane glycoprotein laminin appears to be a critical step in the metastatic process. This binding can be inhibited competitively by a specific pentapeptide sequence (Tyr-Ile-Gly-Ser-Arg) of the laminin B1 chain, and this peptide can prevent metastasis formation in vivo. However, other similar pentapeptide sequences (e.g., Tyr-Ile-Gly-Ser-Glu) have been found to be much less active in metastasis inhibition, raising the possibility that such amino acid substitutions produce structural changes responsible for altering binding to the laminin receptor. In this study, conformational energy analysis has been used to determine the three-dimensional structures of these peptides. The results indicate that the substitution of Glu for the terminal Arg produces a significant conformational change in the peptide backbone at the middle Gly residue. These results have important implications for the design of drugs that may be useful in preventing metastasis formation and tumor spread.

A fluorescence receptor binding assay, based upon the high-affinity fi-adrenergic receptor antagonist propranolol, is utilized to probe the microenvironment of the antagonist-receptor complex in the frog (Rana catesbeiana) erythrocyte membrane. The technique of steady-state fluorescence depolarization is applied to the propranolol-receptor complex, allowing quantitation of the rotational relaxation time of the complex. It is found that the complex is dynamically constrained at 20'C. However, in the temperature range 6-100C a sharp reversible release of constraint is observed. It is further demonstrated that the addition of drugs that are known to specifically disrupt the cytoskeleton (colchicine, vincristine, and vinblastine) causes a similar but irreversible release of constraint at 200C. Cytochalasin B has a much smaller influence on the rotational mobility of the propranolol-receptor complex than do the other drugs that disrupt the cytoskeleton. Amphotericin B is without effect on the rotational constraint of the complex. Binding of the antagonist 13H~dihydroalprenolol is not influenced by colchicine. A model is proposed which postulates that cytoskeletal elements are linked to the antagonist-receptor complex. Antagonist binding does not result in cytoskeleta release, whereas agonist binding is postulated to lead to dissociation of the agonist-receptor complex from the cytoskeleton, thereby activating adenylate cyclase.The importance of the f3-adrenergic receptor system derives from its ubiquitous distribution. The 13-receptor is functionally involved in regulation of processes as diverse as epithelial chloride transport (1) and central nervous system activity (2).It has long been clear that the fl-adrenergic receptor operates through an associated adenylate cyclase, which activity the receptor modulates (3). The molecular mechanism of the receptor-cyclase linkage has been the subject of considerable speculation, and although a number of hypotheses have been advanced, none have been validated or repudiated. Consequently, it is of considerable interest to employ receptor-specific biophysical probes, which allow clarification of the intimate details of the linkage.Propranolol, 1-(isopropylamino)-3-naphthyloxy-2-propanol, is a well-characterized antagonist for the ,3-adrenergic receptor, to which it binds with high affinity (4-6). Its availability as a tritium-labeled compound has made possible its utilization in the characterization of the receptor.The naphthalene nucleus of propranolol makes it a likely fluorescent substrate for the ,B-adrenergic receptor. Many compounds of this general structural type have been applied in the past as fluorescent probes in biological systems (7), and propranolol itself has been shown to fluoresce. This property has in fact been utilized in various pharmacokinetic studies (8,9). We have previously shown (10, 11) that the propranolol fluorescence is sufficiently intense to allow useful determinationThe publication costs of this article were defrayed in part by page char...

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