Penicillamine cyclic enkephalin

Mosberg, H.I., Hurst, R., Hruby, V.J., Gee, K., Akiyama. K., Yamamura, H.I., Galligan, J.J., Burks, T.F. Cyclic penicillamine containing enkephalin analogs display profound delta receptor selectivities, Life Sci 1983, 33 Suppl. 1, 447-50. 

Various peptides from the enkephalin family, or analogs of these molecules, permeate through the blood-brain barrier at different rates, often by different mechanisms [49]. For example, D-Phe-Cys-Tyr-D-Trp-Arg-Thr-Pen-Thr-NH2 (a cyclic peptide that binds to jU.-opioid receptors, in which Pen is penicillamine) permeates by diffusion only Tyr-D-Pen-Gly-Phe-D-Pen ([d-Penj -enkephalin, a cyclic Met-enkephalin analog that binds to 5-opioid receptors) permeates by diffusion and a saturable transport mechanism (Tyr-D-Ala-Gly-Phe-NH)2 (biphalin, a dimeric analog that is active at fx-... 

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