Figure 8: The putative catalytic processing of 10-DAB or DT by DBAT supported by DBAT activity assays after site-specific mutagenesis.

In the catalytic process, His¹⁶² of DBAT acts as a general base catalyst and deprotonates the substrate 10-DAB or DT. (a) For 10-DAB, Gly³⁵⁹, Phe⁴⁰⁰, Arg³⁶³, Gly³⁶¹, Phe⁴⁴ and Ile¹⁶⁴ of DBAT seem to form the substrate binding and/or catalytic sites, as supported by the significant decrease in the activity of the enzyme when these residues are mutated to L-alanine. (b) For DT, Pro³⁷, Gly³⁵⁹, Phe⁴⁰⁰, Arg³⁶³, Gly³⁶¹, Phe⁴⁴ and Ile¹⁶⁴ of DBAT seem to form the substrate binding and/or catalytic sites, due to the significant decrease in the activity after L-alanine scanning mutagenesis. Gly³⁸ and Phe³⁰¹ do not seem to be involved in substrate binding or be part of the catalytic site, and the G38A and F301A mutations increase the activity of DBAT towards DT.