catalytic domain of a polypeptide

of a polypeptide
https://doi.org/10.1351/goldbook.C00892
Any part of a polypeptide chain that possesses a catalytic function. It may contain more than one structural domain.
Source:
White Book, 2nd ed., p. 107 (https://www.qmul.ac.uk/sbcs/iupac/bibliog/white.html)