Modification of skeletal S-1 with fluorescein isothiocyanate

1. Pyridoxal-5'-phosphate (PLP), a marker of primary amines, bound covalently to S-1 in an approximate ratio of 1:1. PLP was localized within the tryptic 25,000 mol. wt fragment. 2. Fluorescein isothiocyanate (FITC), which is known to bind covalently to primary amino groups located at nucleotide binding sites, readily bound to S-1 in a 2:1 ratio. FITC was localized within the 20,000 and 50,000 mol. wt tryptic peptides, in a ratio of 1:1 in each one. 3. These results are consistent with the existence of nucleotide binding sites on myosin different from those of the catalytic sites.