Studies on the mechanisms of histidase development in rat skin and liver. II. Alterations in enzyme levels and synthetic rates during development.

The divergent postnatal developmental courses of histidase catalytic activity in rat liver and skin of the same animals, viz., a progressive rise in hepatic enzyme activity and a simultaneous decline in epidermal activity, has been shown to be accompanied by corresponding alterations in the quantities of the same enzyme protein. These tissue specific developmental changes in enzyme amount have been shown, furthermore, to be a result of selective parallel alterations in histidase synthetic rates. Rates of ³H]leucine incorporation into histidase, isolated by immunoprecipitation, relative to incorporation rates into total soluble tissue protein, increase in liver, while simultaneously decreasing in skin of the same animals during postnatal development.