δ-Aminolevulinic Acid Synthetase Activity in Human Plasma: Relation to Erythropoiesis and Evidence of Induction in Erythropoietic Porphyria

Measurement of δ-aminolevulinic acid synthetase (ALA-S) activity in human plasma has been carried out with samples from normal individuals, cases of erythropoietic porphyria (EP) and erythropoietic protoporphyria (EPP), and of the three principal forms of hepatic porphyria—acute intermittent porphyria, variegate porphyria, and porphyria cutanea tarda. The method of measurement depends on formation of ¹⁴C-ALA when the plasma is incubated with ¹⁴C-succinic acid, succinyl-Co A synthetase, glycine, and other essential substances. The normal samples, as well as those from the hepatic porphyria cases, had small but significant activity of the same extent; those from the erythropoietic group showed consistently higher values, especially in the two cases of congenital type. A remarkably high value in one of these cases in which there was outspoken erythropoiesis was believed to be related to the presence of many fluorescing normoblasts in the peripheral blood. Following multiple transfusions these disappeared concomitantly with striking reduction of the porphyria. The plasma ALA-S activity declined to 1.4% of the pretransfusion value. These results are considered in respect to the question of induction of ALA-S in the developing red cells of the disease, special attention being given to the minor increase of ALA-S activity in the plasma of a nonporphyric individual whose peripheral blood contained large numbers of circulating normoblasts.