The Heme-globin Linkage of Hemoglobin

It was recently reported that CO hemoglobin is relatively more resistant than oxyhemoglobin to digestion by the pancreatic enzymes (l), and that a heme-protein fragment can be precipitated either from the digest solution or from the dialyzed digest by acidification with acetic acid (2). The composition of this CO product has now been investigated. Iron Content-The value of the iron to nitrogen ratio,1 which in early experiments lay near 0.43, was found to vary, figures of 0.39, 0.33, and even 0.21 occurring with later preparations. This ratio is independent of the method by which the product is isolated from the digest solution. Three samples from the same digest, (a) precipitated by acetic acid after dialysis of the digest for 1 day, (6) precipitated after dialysis for 6 days, and (c) precipitated directly without dialysis and washed several times with water, had values of 0.254, 0.258, and 0.263 respectively. The variation in different lots may be due to a gradual inactivation of the crude pancreatin mixture employed (cf. Haurowitz (3)). A sample of CO product with an iron to nitrogen ratio of 0.432 was found to have an arginine content equivalent to one arginine residue per 10.3 atoms of iron. If the protein fragment of the CO product were a low molecular polypeptide, representing the original heme-protein linkage, with arginine as one of its constituent