Kinetic properties of missense mutations in patients with glutathione synthetase deficiency

Patients with hereditary glutathione synthetase (GS) (EC 6.3.2.3) deficienc y present with variable clinical pictures, presumably related to the nature of the mutations involved. In order to elucidate the relationship between genotype, enzyme function and clinical phenotype, we have characterized enz yme kinetic parameters of missense mutations R125C, R267W, R330C and G464V from patients with GS deficiency. One of the mutations predominantly affect ed the K-m value, with decreased affinity for glycine, two mutations influe nced both k(m) and V-max values, and one mutation reduced the stability of the enzyme. This characterization agrees well with predictions based on the recently reported crystal structure of human GS. Thus our data indicate th at different mutations can affect the catalytic capacity of GS by decreasin g substrate affinity, maximal velocity or enzyme stability.