interconvertible enzyme

https://doi.org/10.1351/goldbook.I03081
An enzyme existing in at least two well defined, reversibly convertible forms, produced by covalent modifications of amino acid side chains under biological conditions. Covalent modifications that occur as intermediates in the catalytic process are not included in this definition.
Source:
White Book, 2nd ed., p. 94 (https://www.qmul.ac.uk/sbcs/iupac/bibliog/white.html)