Abstract
Fluorescein isothiocyanate (FITC) is a highly specific inhibitor of rabbit muscle phosphorylase kinase. The rapid inhibition process is accompanied by an almost exclusive incorporation of fluorescein into the α sub‐unit. A molar ratio of 0.8 mol FITC per mol α subunit for a 60% inhibited kinase was calculated. Mg2+ and Mg2+‐ATP completely block the inhibitory effect of FITC, but ATP, ADP and Ca2+ have no significant effect on FITC inhibition. Trypsin‐activated phosphorylase kinase is not inactivated by FITC, while the fluorescein‐modified enzyme can be activated by digestion with trypsin to the same level of activity of trypsin‐activated unmodified enzyme.
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