We have studied the topography of interaction of a family of fluorescent formyl peptides containing four (CHO-Met-Leu-Phe-Lys-fluorescein), five (CHO-Met-Leu-Phe-Phe-Lys- fluorescein), and six (CHO-Nle-Leu-Phe-Nle-Tyr-Lys-fluorescein and CHO-Met-Leu-Phe-Phe-Phe-Lys- fluorescein) amino acids with their receptor using spectroscopic methods adapted to small sample volumes. Only the fluorescent peptides containing four and five amino acids were quenched upon binding to the receptor, indicating physical contact of the chromophore with the receptor. In contrast, only the hexapeptides were accessible to antibodies to fluorescein. Taken together, these results suggest that the carboxy terminus of the tetrapeptide or the pentapeptide is protected in the receptor binding pocket while the fluorescein on the carboxy terminus of either hexapeptide is exposed and recognized by the antibody to fluorescein. These results indicate that the binding pocket accommodates at least five but no more than six amino acids.
Notes nature of the product are consistent with such a mechanism.
Experimental SectionThe tert-butyl amidosulfite 2 prepared by the method of Deyrup and Moyer2 had bp 60-62' (0.4 mm) [lit.2 bp 70-75O (0.3 mm)]. Kinetics were followed at 276 nm using a Durham-Gibson stopped-flow spectrophotometer. Optical densities were measured on the photograph of the oscilloscope trace and rate constants determined graphically. The values of k~ in Table I are the average of several runs at each acid concentration, Average deviation from the mean is less than 5%. Initial concentration of amidosulfite in kinetic runs was ca.M.
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