Calcium/calmodulin alleviates substrate inhibition in a strawberry UDP-glucosyltransferase involved in fruit anthocyanin biosynthesis

Table 1 Effect of calmodulin on FvUGT1 kinetic parameters toward pelargonidin

CaM (μM)	V _max (nmol · s⁻¹ · mg⁻¹)	K _m (μM)	K _i (μM)	V _i (nmol · s⁻¹ · mg⁻¹)	n	r ²
0	12.6 ± 0.95^a	70.1 ± 3.0^a	331.5 ± 13.3^b	3.3 ± 0.35^a	1.5 ± 0.12^a	0.99
0.1	21.6 ± 1.88^b	147.4 ± 20.9^b	359.6 ± 22.7^bc	4.0 ± 0.22^b	1.2 ± 0.05^b	0.99
0.5	41.2 ± 3.0^c	288.2 ± 20.4^c	294.3 ± 18.5^a	5.0 ± 0.48^c	1.2 ± 0.10^b	0.99
2.5	43.6 ± 2.2^c	403.5 ± 29.8^d	386.4 ± 20.0^c	4.7 ± 0.18^c	1.1 ± 0.01^b	0.99

Note: The reaction mix included 5 mM UDP-Glc, fixed concentrations of calmodulin (01, 0.5 and 2.5 μM, respectively), and 0–1,400 μM pelargonidin chloride. Different letters (a, b, c, d) in all the parameters indicate significant differences among mean values (P < 0.05; t-test). The results are based on at least three repeats in three independent experiments. CaM: calmodulin; V _max: the maximal reaction rate; K _m: the substrate concentration at which the reaction rate is half of V _max; K _i: the inhibition constant which is the concentration of inhibitor required to decrease the maximal rate of the reaction to half of the uninhibited value; V _i: the reaction velocity in the presence of inhibition; n, x: Hill coefficient

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