Table 1. Kinetic parameters of P. trichocarpa PtAAS1, PtAAS2, PtAADC1, PtAADC2, and PtAADC3

Enzymes were heterologously expressed in E. coli, purified, and incubated with Phe, Tyr, or Trp. Kinetic parameters are shown as means ± se (n = 3). Volatile phenylacetaldehyde was analyzed via TDU-GC-MS; all other compounds were measured using LC-MS/MS. PHA, phenylacetaldehyde; PEA, 2-phenylethylamine; 4-OH-PHA, 4-hydroxy phenylacetaldehyde; IAAld, indole-3-acetaldehyde; TyrA, tyramine; TrpA, tryptamine.

EnzymeSubstrateProductKm (mm)Vmax (nmola µg−1a min−1)kcat (s−1)kcat /Km (s−1 mm−1)
PtAAS1PhePHA0.46 ± 0.02
PhePEA
Tyr4-OH-PHA
TrpIAAld
PtAAS2PhePHA0.69 ± 0.39
PhePEA
Tyr4-OH-PHAadetected
TrpIAAldadetected
PtAADC1PhePHA
PhePEA0.17 ± 0.03430 ± 120.392.3
TyrTyrA2.0 ± 0.285.4 ± 3.90.080.04
TrpTrpA3.0 ± 0.47.7 ± 0.50.0070.002
PtAADC2PhePHA
PhePEA0.19 ± 0.010.89 ± 0.010.814.2
TyrTyrA1.2 ± 0.2148 ± 70.140.11
TrpTrpA
PtAADC3PhePHA
PhePEA2.3 ± 0.26.7 ± 0.20.140.003
TyrTyrA0.043 ± 0.0043.61 ± 0.060.0030.08
TrpTrpA
  • a Compounds were chemically converted into the corresponding aldoximes before LC-MS/MS analysis (see “Materials and Methods”).