**2. Materials and methods**

## **2.1 Materials**

*D*-LH2 potassium salt was obtained from Europa Bioproducts and *D*-ALH2 from Marker Gene Technologies Inc. (Eugene, OR, USA). x2 Fluc was donated by Dr. Peter White (Dstl, Porton Down, Salisbury, UK) [White *et al.*, 2002; Willey *et al.*, 2001]. Ultra-GloTM luciferase (UG) was purchased from Promega and all other chemicals were purchased from Melford Laboratories Ltd. or Sigma-Aldrich unless otherwise specified.
