Table 2.

Catalytic efficiencies of extant and ancestral enzymes.

enzyme (and substrate)	organism	age (years)	kcat/KM (s−1 M−1)	references
thioredoxin	E. coli	extant	2.5 × 105	[3]
	H. sapiens	extant	5.2 × 105
	ancestor of Eukarya	1.6 × 109	7.6 × 105
	ancestor of Archaea	4.1 × 109	8.2 × 106
	ancestor of Bacteria	4.2 × 109	4.7 × 105
nucleoside diphosphate kinase	A. fulgidus	extant	1.2 × 106	[4]
	archaeal ancestor Arc5	3.8 × 109	4.0 × 106
isopropylmalate dehydrogenase	B. subtilis	extant	7.5 × 104	[5,6]
	B. caldovelox	extant	4.8 × 104
	ancestor of Bacillus	9.5 × 108	2.1 × 105
	ancestor of Firmicutes	2.6 × 109	1.1 × 105
uricase	S. scrofa	extant	3.6 × 105	[7]
	ancestor of mammals	9.4 × 107	7.1 × 105
ribonuclease A	E. coli	extant	5.0 × 106	[76]
	artiodactyls	3.0 × 107	3.3 × 106
chymase	H. sapiens	extant	3.6 × 106	[8]
	ancestor of mammals	NRa	4.3 × 106
α-glycosidase (maltose)	L. elongisporus	extant	6.2	[9]
	yeast ancestor	1.2 × 108	13.0
α-glycosidase (maltotriose)	L. elongisporus	extant	1.7	[9]
	yeast ancestor	1.2 × 108	19.2
α-glycosidase (sucrose)	L. elongisporus	extant	11.0	[9]
	yeast ancestor	1.2 × 108	31.6
β-lactamase (benzylpenicillin)	E. cloacae	extant	2.6 × 107	[69]
	‘GPBCA’ ancestorb	1.5 × 109	7.0 × 106
	‘PNCA’ ancestorb	3.0 × 109	5.0 × 105
β-lactamase (cefotaxime)	E. cloacae	extant	2.6 × 103	[69]
	‘GPBCA’ ancestorb	1.5 × 109	3.7 × 104
	‘PNCA’ ancestorb	3.0 × 109	1.0 × 106
β-lactamase (ceftazidime)	E. cloacae	extant	6.5 × 102	[69]
	‘GPBCA’ ancestorb	1.5 × 109	5.0 × 103
	‘PNCA’ ancestorb	3.0 × 109	3.0 × 104

^aNR: not reported, although by analogy with [7] this ancestor is assumed to have an age of approximately 9.4 × 10⁷ years.

^bAbbreviations are as used in [69]. GPBCA, last common ancestor of Gammaproteobacteria; PNCA, last common ancestor of various Gram-positive and Gram-negative bacteria.