On the haematin compound of peroxidase

It was shown previously (Keilin 1927) that horseradish roots contain a large concentration of haematin which can easily be seen spectroscopically as pyridine-haemochromogen in slices of roots 5-10 mm. thick which have been treated with pyridine and Na2S2O4. Similar haematin compounds are widely if not universally distributed in cells and tissues of all aerobic organisms where they can be observed in addition to or in absence of the haematin of cytochrome (Keilin 1925).