DNA, RNA and protein metabolism was investigated by means of a high resolution autoradiographic technic in normal and acute leukemia blast cells by studying the incorporation of tritiated thymidine, uridine, leucine and phenylalanine. A strikingly lower percentage of cells labelled with thymidine was demonstrated in acute leukemia and was interpreted as evidence of a decreased proliferative capacity. A very significantly lower uptake of uridine, leucine and phenylalanine was detected in acute leukemia cells.

In normal and leukemic cells, amino acid incorporation occurred both in the nucleus and in the cytoplasm; uridine was incorporated exclusively in the nucleus during the first hour of incubation and the cytoplasm became labelled only in a later period.

The constant ratio between uridine and amino acid incorporation detected in normal myeloblasts was always altered in acute leukemia cells.

The lower RNA and protein metabolism and its dissociation in acute leukemia cells was discussed as related to the well-known maturation defect of these cells.

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