Table I. Mutational analysis of GP42 reveals amino acid residues indispensable for both TGase and elicitor activities^a.

Protein	TGase activity (mOD/min/µg)	Elicitor activity [EC50 (nM)]
WT TGase	104.0 ± 22.8	0.5
W231A	1.5 ± 1.3	–b
P234A	6.5 ± 2.6	11.2
Y241A	98.9 ± 2.2	1.1

^aElicitor activity of TGase is expressed as the EC₅₀ value, which corresponds to the protein concentration required to half-maximally stimulate phytoalexin production in parsley protoplasts (Parker et al., 1991).

^bNo detectable activity (tested up to 50 nM).