In addition, there has been evidence showing the presence of "pseudoperoxidase
" or peroxidase-like activities in hemoglobins [3-8].
The principle of the method for GPx activity measurement was based on recording the decrease in absorbance of NADPH at 340 nm using [H.sub.2][O.sub.2] and reduced glutathione as substrates, in the presence of yeast glutathione reductase and Na[N.sub.3] to inhibit the pseudoperoxidase
activity of Hb.
The gFOBT has a long history of use for detecting the presence of blood in the stool and is based on the pseudoperoxidase
activity of heme in human hemoglobin.
[H.sub.2][O.sub.2] is toxic to the cells and recently it has been shown that Hb also possesses antioxidative pseudoperoxidase
This method detects the pseudoperoxidase
activity of hemoglobin; thus, endogenous salivary peroxidases produce false-positive results for hemoglobin.
Ascorbic acid as an antioxidant may yield false negative results when it interferes with the pseudoperoxidase
This procedure inhibited endogenous AP, peroxidase, and pseudoperoxidase
activity present in tissues.
It is also relevant to mention that above-therapeutic concentrations of mesna, which carry a high reducing capacity, did not cause interference in two Chemstrip 10UA tests that are based on oxidation reactions (glucose by glucose oxidase/peroxidase and hemoglobin with its strong pseudoperoxidase
A second obstacle was the pseudoperoxidase
activity of hemoglobin, which can catalyze side reactions with hydrogen peroxide.
A microhematuria/hemoglobinuria assay performed at the same time utilizes the pseudoperoxidase
activity of hemoglobin.