Biochemical assays of hemoglobin in normal human erythroid clones

Quantitation of small amounts (2-3 micrograms) of hemoglobin (Hb) was achieved by each of three spectrophotometric techniques. An assay employing benzidine base consistently underestimated Hb at this level and gave a wide scatter of results at higher values. The cyanmethemoglobin method was at the limit of its sensitivity and suffers from the disadvantage of having high optical densities in the blank samples. By contrast, pyridine hemochromogen can be detected accurately with 200 ng of Hb (equivalent of 6,000 mature erythrocytes), and the regression line with this technique virtually passes through the origin. Furthermore, the extinction coefficient of pyridine hemochromogen in the Soret band is 13.5-fold greater than that of cyanmethemoglobin. In normal human erythroid clones, generated in vitro from bone marrow cells, mean cell hemoglobin (MCH) values were determined after various intervals of culture. The MCH after 5, 7, 10, and 14 days were 11.8, 15.8, 26.6, and 34.4 pg, respectively, by the pyridine hemochromogen method. Reaction product was also identified in granulocyte-macrophage clones, presumably reflecting the content of other heme proteins such as catalase and cytochromes. Account must be taken of this non-Hb material in computing true MCH values for erythroid cells.