To pair a predicted reaction with possible enzymes, a trained transformer computes the predicted amino acid sequences, which are compared with all available enzymes in the pool. Eq. 9 A Levenshtein distance threshold of 64.6 -the mean value in test dataset, between the predicted sequence and available sequences was used to measure the possibility of enzyme promiscuity. For a given predicted reaction, possible promiscuous enzymes below this threshold were sorted by Levenshtein distance to rank the likelihood to catalyse the predicted reaction. Reactions with no enzyme suggested were removed from the predicted reaction dataset. The transformer model prediction for the predicted reaction example of glycosylation of mandelonitrile is shown in Figure . From the final trained model, an amino acid sequence with length of 528 is predicted for the predicted reaction SMILES. Using the Levenshtein distance to filter the invalid enzymes, only enzyme prunasin hydrolase (EC 3.2.1.118) falls into the possible promiscuous enzyme list, with Levenshtein distance of 47.