Ornithine decarboxylase in rat skin.

Ornithine decarboxylase (ODC; E.C.4.1.1.17) activities can be stimulated 2-10 fold in rat epidermis and dermis by hair plucking. Stimulation does not involve the removal of a soluble ODC inhibitor. ODC activity in the dermis and whole skin decreased with aging, while the epidermis showed little change. The apparent Km for ornithine and the heat stability of ODC in plucked and unplucked skin were similar. ODC was assayed in plucked and unplucked skin of rats fed diets containing between 2 and 24% protein. Activities in both plucked and unplucked skin were higher in the animals fed diets with higher protein contents. ODC levels were positively correlated with the weight changes undergone by rats on controlled-protein diets. In animals restricted to 2% protein diets and rehabilitated with 16% protein diets, enzyme levels were increased after 2 days rehabilitation and peaked after 5 days rehabilitation. The responsiveness of ODC to changes in dietary protein may be useful in the diagnosis of protein malnutrition.