Table 2. Summary of specificities of several characterised GH27 enzymes, and motivation for the mutations of CpArap27.

CpArap27 variant form		Equivalent previously characterised enzyme
Enzyme	Ara:Gal ratio a	Enzyme	k cat / K m	Ara:Gal ratio a
Wild-type	Ara only	GsAbp	Ara:495 [42]	Ara (trace pNP-α-D-Galp, pNP-α-L-Araf)
I56E	Ara only	SaArap27A	Ara:88.1 Gal:0.5 [41]	196:1
I56D	142:1	ScaGal	Gal:63.6 [21]	Gal only
I56D	142:1	SaArap27A E99D	Ara:1.5 Gal:6.7 [41]	1:4.4
I56C	1:2.2	FoAp1	Ara:9.2 Gal: 9.9 [50]	1.1:1
I56C	1:2.2	FoAp2	Ara:8.1 Gal:0.6 [50]	13.6:1
I56A	1:1.4	No examples	-	-

Kinetic parameters for several GH27 enzymes, with different substrate specificities and different amino acids in a key active site position, are compared. Kinetic parameters for all forms of CpArap27 are given in Table 1. The Ara:Gal ratios were determined by dividing k _cat / K _m values and normalising the smaller value to 1.

^a The Ara:Gal ratio of each enzyme or enzyme variant compares k _cat / K _m for hydrolysis of pNP-β-l-Arap and pNP-α-d-Galp respectively.