Abstract: | Leucine9-α-melanotropin ([Leu9]α-MSH) was synthesized in homogeneous solution by a fragment condensation approach, and it was assayed for its melanophore-dispersing and its tyrosinase-stimulating activity with a reflectometric in vitro frog skin assay and with cultured mouse melanoma cells, respectively. In both assay systems, parallel log dose-response curves were obtained for ([Leu9)]α-MSH and α-MSH; however, in the frog skin assay the activity of the title compound was 1 middot; 1010 Units/mmol, i.e. 25% of the activity of α-MSH, whereas its tyrosinasestimulating potency was only 1% compared to α-MSH (EC50= 2.5 · 10?7M ). This indicates a major difference in the recognition/stimulation process of the receptors of the two cell types. |