Pyrrolidone Carboxylic Acid Synthesis in Guinea Pig Epidermis

Abstract

To establish the in vivo mechanism of synthesis and accumulation of epidermal pyrrolidone carboxylic acid (PCA), enzymes potentially capable of PCA synthesis have been quantified and located within the guinea pig epidermis. Intermediates in the synthesis of [3H]PCA from a pulse of [3H]glutanilne have been identified and quantified to determine which of the several possible metabolic routes occurs in vivo. PCA appears to be synthesized from substrate derived from the breakdown within the stratum corneum of protein synthesized several days earlier. The predominant route is probably via the nonenzymic cyclization of free glutamine liberated from this protein. In view of the high activity of γ-glutamyl cyclotransferase in the stratum corneum, a minor contribution to PCA formation by the action of the enzyme on γ-glutamyl peptides cannot be excluded