14C-glycine and methionine were injected into the lesions of patients with psoriasis and pityriasis rubra pilaris and into the clinically unaffected skin between the lesions. The transit time of both amino acids was greatly increased in the lesions. Between the lesions the peak isotope loss was greater for both amino acids and significantly earlier for methionine. These findings indicate a rapid epidermal replacement in the lesions in both diseases but in the intervening skin the technique does not distinguish between rapid epidermal proliferation and an abnormality in the site of amino-acid incorporation.
Porter D, Shuster S. Epidermal Renewal and Amino Acids in Psoriasis and Pityriasis Rubra Pilaris. Arch Dermatol. 1968;98(4):339-343. doi:10.1001/archderm.1968.01610160013003