Table 2.

Specific enzyme activities of homogeneously purified recombinant DHS and HSS from S. vernalis

Substrate		Specific activity (pkat/mg)
Aminobutyl donor (μM)	Aminobutyl acceptor (μM)	DHS	HSS
Spermidine (40)	eifsv1 (40)	318	ND*
Spermidine (40)	Putrescine (40)	138	590
Spermidine (400)	Putrescine (400)	737	3206

Enzyme assays were performed under identical conditions in the presence of 1 mM NAD⁺ and two different substrate concentrations: (i) 40 μM, which is saturating and optimal in the DHS assay with eifsv 1 as substrate (eifsv 1 concentrations >40 μM cause substrate inhibition), and (ii) 400 μM, which is saturating in the HSS assay with putrescine (11). 

*ND, not detectable.