Table 1.

Mammalian PLP-dependent enzymes with L-cysteine S-conjugate β-lyase activity^a

	β-Lyase substrates			Syncatalytic inactivation	Competing transamination	Approximate specific activity (U/mgb)
	DCVC	TFEC	BTC
Enzyme (cytosolic)
Kynureninase (R)	+	ND	+	+	ND	0.25
GTK/KAT I (R)	+	+	−	−	+	0.6 – 6.4
GTK/KAT I (H) c	+	+	+	−	+	8 – 40
cAAT (R)	+	+	±	+	−	0.04 – 0.16
AlaAT (P)	+	+	+	+	−	0.004 – 0.06
BCATc (H)	+	+	+	+	−	0.3 – 0.5
Cystathionine γ-lyase (R)	−	+	−	−	−	0.05 – 0.1
High-Mr β-lyase (R)d		+	+	−	+	~0.07-1.0
Enzyme (mitochondrial)
mAAT (R)	+	+	+	+	+	0.8 – 2.3
BCATm (H)	+	+	−	+	−	0.2 – 0.5
AGAT II (R)	+	+	+	+	+	0.2
GABA aminotransferase (P)	ND	+	ND	ND	ND	0.016
High-Mr β-lyase (R)e	+	+	+	ND	+	0.1 – 1.2

^aThis table is an update of that of Cooper and Pinto (2006) as modified by Cooper and Hanigan (2010). For original references see Cooper and Pinto (2006). A unit of enzyme activity (U) is defined as the amount of enzyme that catalyzes the formation of 1 μmol of pyruvate per min (usually at 37°C, but temperature was not always specified). The specific activities are from published data on highly purified enzymes. ND, not determined. Species abbreviations: R, rat; P, pig; H, human.

^bActivity with DCVC and/or TFEC.

^cFrom Cooper et al. (2008a). Some GTK activity is also found in rat kidney and liver mitochondria, but the role of mitochondrial GTK as a cysteine S-conjugate β-lyase is uncertain.

^dContains GTK activity

^eContains mAAT activity