Cellular mechanisms of protein metabolism in the nephron. II. The histochemical characteristics of protein absorption droplets.

Histochemical methods show not only the presence of absorbed protein in the cellular droplet, but also the general identity of its constituent substances with those of the mitochondrial rodlets. Both contain considerable amounts of phospholipid and probably some PNA. The reactivity of the cytoplasmic constituents in droplet and in rodlet are different, however, since in the droplet these substances stain more intensely. As judged by variations observed in this intensity during the evolution of the droplet, these constituents and the absorbed protein vary in their proportions and amount. The droplet would appear to be a highly active center of protein metabolism.