Enzymes are biological catalysts Enzymes affect reaction rates,not equilibria. HO Orotate decarboxylase Kat=39S-1→25×103 second Kon=2.8×1016S-1→78×105year Kcat/knon=1.4×1017 4 4 Orotate decarboxylase Knon = 2.8 10-16 S -1 ➔ 78  106 year Kcat= 39 S-1 ➔ 25  10-3 second Kcat / knon = 1.4  1017 Enzymes are biological catalysts. Enzymes affect reaction rates, not equilibria