= Phenazine methosulfate
\b[Phenazine methosulfate] is a salt containing a methylphenazinium cation and a methyl sulfate counterion. Its overall formula is $\mathrm{C_{14}H_{14}N_2O_4S}$. The redox-active phenazinium system makes the compound useful as an artificial <electron carrier> in coupled biochemical measurements.<Phenazine methosulfate in PubChem>[CID9285, component compounds, structure and formula]{ref}
The original <methanol dehydrogenase> work used <phenazine methosulfate> between the enzyme reaction and an optical readout involving <DCPIP>. A reducing equivalent transferred from substrate through the carrier can reduce the dye, so a change in <absorbance> reports the coupled system. The investigators used a <spectrophotometer> with 10-mm optical paths and calibrated the dye's absorption at 600 nm.<The microbial oxidation of methanol. 2. The methanol-oxidizing enzyme of Pseudomonas sp. M 27 by C. Anthony and L. J. Zatman>[p.614, Materials and Methods, Spectrophotometry and dye standardization]{ref}
An original measurement example separates concentration from mechanism. Suppose a dye's initial <absorbance> is 0.80 and its corrected final <absorbance> is 0.40. If the <Beer-Lambert law> applies with unchanged <optical path length> and coefficient, the absorbing dye concentration has halved. That observation alone does not determine the concentration of the enzyme or prove which substrate supplied the electrons.
The carrier and reporter are separate experimental components. Controls without enzyme or without substrate help distinguish the intended coupled reaction from background <reduction>. A carrier compatible with one enzyme system is not automatically the natural physiological electron acceptor of that enzyme.
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