||Malinen AM et al., Active site opening and closure control translocation of multisubunit RNA polymerase. Nucleic Acids Res. 2012 Aug40(15):7442-51. doi: 10.1093/nar/gks383. p.7445 right column 2nd paragraphPubMed ID22570421
||Webb MR. A continuous spectrophotometric assay for inorganic phosphate and for measuring phosphate release kinetics in biological systems. Proc. Natl Acad. Sci. USA 1992 89 :4884-4887.PubMed ID1534409
||p.7445 right column 2nd paragraph:"On the other hand, it is not clear how an assay based on purine ribonucleoside phosphorylase, an enzyme with a turnover number of 40?s^-1 and Km of 26?µM (primary source), can be used to monitor the millisecond timescale release of nanomolar concentrations of Pi and output rates as high as 500–600?s^-1 (ref 28)."