Diverse allosteric and catalytic functions of tetrameric d-lactate dehydrogenases from three Gram-negative bacteria

AMB Express

Table 1 Kinetic parameters for various 2-ketoacids at pH 7.0 ^a

	k_cat(s^-1)	S_0.5(mM)	k_cat/S_0.5(s^-1 mM^-1)	K_i(mM)^b	n _H ^c
Glyoxylate
FNLDH	11 (0.1)	18 (0.4)	0.70 (0.007)
PALDH	880 (60)	6.8 (0.6)	130 (5)	44 (8)
ECLDH	100 (5)	20 (2)	5.3 (0.2)		1.5 (0.09)
Pyruvate
FNLDH	80 (0.4)	0.34 (0.007)	230 (4)
PALDH	400 (10)	0.10 (0.009)	4,000 (300)	1.8 (0.1)
ECLDH	410 (8)	2.6 (0.09)	160 (2)		1.4 (0.05)
2-Ketobutyrate
FNLDH	140 (0.7)	0.31 (0.006)	440 (7)
PALDH	100 (0.6)	0.64 (0.01)	150 (3)
ECLDH	31 (2)	30 (4)	1.0 (0.05)		1.4 (0.08)
2-Ketovalerate
FNLDH	140 (0.5)	0.68 (0.01)	200 (3)
PALDH	69 (0.5)	4.0 (0.07)	18 (3)
ECLDH	N.D.^d	N.D.	<0.01
2-Ketoisovalerate
FNLDH	120 (0.7)	3.5 (0.07)	35 (0.5)
PALDH	N.D.	N.D.	<0.4
ECLDH	N.D.	N.D.	<0.01
2-Ketocaproate
FNLDH	230 (1)	2.6 (0.06)	87 (1)
PALDH	160 (1)	5.8 (0.1)	27 (0.4)
ECLDH	N.D.	N.D.	<0.01
2-Ketoisocaproate
FNLDH	200 (2)	3.8 (0.1)	53 (1)
PALDH	39 (0.3)	12 (0.2)	3.2 (0.03)
ECLDH	N.D.	N.D.	<0.01
Oxaloacetate
FNLDH	80 (1)	2.5 (0.09)	31 (0.7)	140 (20)
PALDH	410 (4)	1.7 (0.06)	230 (6)
ECLDH	1,100 (200)	54 (10)	21 (0.6)	5.0 (1)
Hydroxypyruvate
FNLDH	160 (2)	18 (0.4)	8.7 (0.07)
PALDH	420 (10)	3.0 (0.2)	140 (3)	19 (1)
ECLDH	50 (0.5)	12 (0.3)	4.2 (0.06)
Phenylpyruvate
FNLDH	120 (7)	11 (0.9)	11 (0.3)	23 (3)
PALDH	18 (0.2)	7.1 (0.2)	2.6 (0.04)
ECLDH	N.D.	N.D.	<0.01
Hydroxyphenylpyruvate
FNLDH	N.D.	N.D.	<0.02
PALDH	N.D.	N.D.	<0.4
ECLDH	N.D.	N.D.	<0.01

^aParameters were determined as described in the `Materials and methods' section, and standard deviations are shown in parentheses. ^bThe inhibition constants (K_i) and ^cHill coefficients (n_H) are shown only for the cases in which significant substrate inhibition and cooperativity were observed, respectively. ^dN.D., not determined. The activities were too weak for determination of exact values.