7-Methyl-6-thioguanosine (MESG, Abs = 330 nm) forms 7-methyl-6-thioguanine (Abs = 355 nm) in the presense of inorganic phosphate and purine nucleoside phosphorylase (PNP) and thus constitutes a rapid and sensitive assay for phosphate. If inorganic pyrophosphatase is present, MESG may also be used to detect inorganic pyrophosphate.⁽¹⁾ MESG should be used as soon as possible after dissolution.

Ref:

1. (a) Webb, M. R. PNAS 1992, 89, 4884-4887. (b) Wedler, F. C.; Ley, B. W.; Moyer, M. L. Anal. Biochem. 1994, 218, 449-453. (c) Cheng, J.; Farutin, V.; Wu, Z.; Jacob-Mosier, G.; Riley, B.; Hakimi, B.; Cordes, E. H. Bioorg. Chem. 1999, 27, 307-325.