Datensatz

Zusammenfassung

Tryptophan hydroxylase (TPH) catalyses the first and rate limiting step in the biosynthesis of the neurotransmitter serotonin. There are two TPH isoenzymes in humans, encoded by two different genes: TPH1 and the recently described TPH2. We have expressed both human enzymes and various deletion mutants of TPH2 (ΔN44, ΔC17, ΔC19, ΔC51) in COS7 cells. TPH1 and 2 displayed different kinetic properties with a lower Km value of TPH1. Removal of 44 amino acids from the N-terminus of TPH2 resulted in a 3–4-fold increased Vmax, which indicates a strong inhibitory function of this part on the enzymes activity. TPH1 and 2 were able to form homooligomers and also heterooligomers with each other. The different deletion mutants (ΔC17, ΔC19 and ΔC51), which lack the putative C-terminal leucine zipper tetramerization domain, existed as monomeric enzymes. While short deletions (ΔC17 and ΔC19) hardly changed Vmax values, the ΔC51 mutant lost 99% of TPH activity. These data identify a region between the C-terminal oligomerization domain and the catalytic domain, which is indispensable for TPH2 activity.