Abstract
The "light" mitochondrial pellet obtained from the kidneys of rats previously treated with Triton WR-1339 and rendered hypoxic was separated into subcellular component fractions by sucrose density gradient centrifugation in a zonal rotor. Selected fractions were pooled, disrupted by osmotic lysis and repeated freeze-thawing, and incubated in the presence and absence of normal rat serum. The incubation mixtures were assayed for erythropoiesis-stimulating activity (erythropoietin). High specific activity was identified only in fractions rich in lysosomes. Biochemical analysis of reference enzymes for the identification of lysosomes and mitochondria, supplemented by electron microscopic examination of the various separated fractions, supports the observed requirement for lysosomal constituents in the formation of erythropoietin by the kidney.
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