Table 4.
Kinetic Parameters of Recombinant XAT
| Enzyme | Reaction | Substrate | Km (μM) | Reference |
|---|---|---|---|---|
| XAT | Transesterification | Lutein (xanthophyll) | 60.2 ± 7.6a | This work |
| XAT | Transesterification | Trilinolein (TAG) | 50.6 ± 27a | This work |
| XAT | Hydrolysis (lipase) | p-nitrophenyl palmitate | 160 ± 67a,b | This work |
| XAT | Hydrolysis (esterase) | p-nitrophenyl acetate | 474 ± 94a | This work |
| CD1 | Transesterification | 2-mono-(10,16-dihydroxyhexadecanoyl) glycerol | 925 ± 98 | Yeats et al., 2014 |
| BS1 | Hydrolysis | 2,3,4-tri-O-acetyl-methyl β-D-xylopyranoside | 4400 ± 780 | Zhang et al., 2017 |
Km was calculated using Michaelis-Menten plots using 20 μg recombinant protein for lutein, 52 μg for the TAG substrate and 10 μg of XAT for both the nitrophenyl ester substrates. Kinetic data previously calculated for reactions catalyzed by other plant GDSL esterase/lipases, tomato CD1 and rice BS1, have also been included. CD1 is part of the same phylogenetic clade as XAT, Clade IV as designated by Chepyshko et al., (2012; see Figure 2), whereas BS1 is from Clade I of the GELP family.
a
Statistically significant difference (P < 0.05).
b
Apparent Km value, as reaction preceded too fast to observe kinetics at low concentration of substrate.