Bisfunction of propionic acid on purified rat liver β‐ureidopropionase

Propionic acid and isobutyric acid, which are structural analogues of N ‐carbamoyl‐β‐alanine and N ‐carbamoyl‐β‐aminoisobutyric acid, respectively, acted as an allosteric activator as well as a competitive inhibitor of purified rat liver β‐ureidopropionase. Propionic acid and isobutyric acid had a K i value of approx. 0.3 mM at pH 7.0. The Hill coefficient for N ‐carbamoyl‐β‐alanine was 2.0, but the cooperativity decreased to 1.0 in the presence of 1 mM propionic acid. The K value towards N ‐carbamoyl‐β‐alanine was calculated to be 0.17 mM from Hill plots and the K m value was determined to be 0.06 mM from replots of the apparent K m vs propionic acid.