Millimolar absorptivity of ZnPROTO in pyridine, 221, and acetone containing 8.2% of 0.5-mole aqueous acetic acid per liter, 211, has been determined on a sample characterized by chromatography, fluorescence spectroscopy, nuclear magnetic resonance spectroscopy, and elemental analysis. These values are substantially higher than previously reported values. A quantitative fluorometric micromethod specific for ZnPROTO in blood is reported. This method gives results equivalent to an FEP method when ZnPROTO is the only species of porphyrin present. If PROTO is also present, the FEP method which measures both, gives a high result. The fraction of PROTO may be calculated from the difference between the FEP and ZnPROTO. In healthy young children with ZnPROTO only, PbB {precedes above single-line equals sign} 26 and hematocrit {succeeds above single-line equals sign} 36%, the following average values were found: ZnPROTO, 1.28 μm per liter of erythrocytes; FEP, 1.24 μm per liter of erythrocytes. Observations in patients show that protoporphyrin is not the only condition in which the concentration of PROTO in erythrocytes is elevated. Increase in PROTO has been found in sickle cell (SS) disease, cord blood from newborns, and in anemic iron deficient children with and without increased lead absorption. Density gradient studies in human cord blood show that PROTO is found in the reticulocyte-rich fraction, as has been reported by others in studies of patients with iron deficiency anemia. The quantitative micromethod for ZnPROTO described here, if used in conjunction with both a standard FEP method and spectrophoto-fluorometry, may prove useful in exploring the significance of elevations in PROTO in these varied clinical conditions. © 1979.
