Exploring the in Vitro Operating Window of Glycosyltransferase PtUGT1 from Polygonum tinctorium for a Biocatalytic Route to Indigo Dye

The eobiotic compound indican lends itself to a compelling biocatalytic dyeing strategy for denim, in which the formation of corrosive byproducts is avoided. However, the efficient and scalable production of indican remains a key bottleneck. This work focuses on the in vitro characterization of PtUGT1, a glycosyltransferase from Polygonum tinctorium that catalyzes the formation of indican via the glycosylation of indoxyl. Here, the buffer composition and enzyme concentration were identified as key parameters for enzyme activity and stability. The short lifetime of the enzyme under reaction conditions initiated an immobilization study. As a consequence, an amino-functionalized methacrylate resin was identified as a highly functional option for efficient immobilization of PtUGT1, allowing immobilization yields of >98% for enzyme loadings up to 7.6 wt %. We further report a stabilization factor of 47 and significantly improved overall biocatalytic productivity. The straightforward handling and reuse of the described heterogeneous biocatalyst is demonstrated.