Proanthocyanidin accumulation and transcriptional responses in the seed coat of cranberry beans ( Phaseolus vulgaris L.) with different susceptibility to postharvest darkening

Table 4 Kinetic parameters for PvANR1 in assays containing varying amounts of cyanidin and NADPH

Varying substrate	Product	K _0.5 (μM)	K _i (μM)	V _max (nmol min⁻¹ mg⁻¹)	k _cat (s⁻¹)	k _cat /K _0.5 (s⁻¹ M⁻¹)
Cyanidin	Epicatechin^a	114.2 ± 19.0	631.5 ± 119.9	11.57 ± 1.13	0.0072 ± 0.0007	65.4 ± 13.8
Cyanidin	Catechin^a	116.5 ± 10.7	583.8 ± 116.1	8.32 ± 0.73	0.0052 ± 0.0004	45.4 ± 6.42
NADPH	Epicatechin^b	103.5 ± 7.4	-	3.34 ± 0.21	0.0021 ± 0.0001	20.1 ± 0.49
NADPH	Catechin^b	102.3 ± 7.8	-	2.44 ± 0.18	0.0015 ± 0.0001	14.9 ± 1.03

The K _cat (also referred to as turnover rate) was calculated using a molecular mass of 37.4 kDa for the final recombinant PvANR1 preparation, following removal of the His₆ tag
^aA non-linear regression model for substrate inhibition (as described under Methods) was used to determine apparent kinetic parameters for cyanidin. These assays were performed at a fixed NADPH concentration of 800 μM
^bThe Hill equation was utilized to determine kinetic parameters for NADPH. These assays were performed at a fixed cyanidin concentration of 100 μM; the Hill coefficient for epicatechin and catechin formation was 2.5 ± 0.19 and 2.5 ± 0.15, respectively

ISSN: 1471-2229