Serine biosynthesis in human hair follicles by the phosphorylated pathway: follicular 3 phosphoglycerate dehydrogenase

Abstract

The phosphorylated pathway of serine biosynthesis was demonstrated in human hair bulbs and sheaths by the formation of phosphoserine and serine from [14C]3 phosphoglyceric acid. The initial and rate limiting enzyme of the pathway, 3 phosphoglycerate dehydrogenase (3 PGDH) was demonstrated by enzyme determinations in human and rat hair follicles, human epidermis, and chicken epidermis. Follicular 3 PGDH was characterized using a sensitive fluorometric assay with NADH as a cosubstrate. Monovalent cations (Na+, K+, Li+, or NH4+) were necessary for full enzyme activity. p Hydroxymercuribenzoate inhibited activity, and activity was 3 times higher with NADH as a cosubstrate than with NADPH. The apparent Km for the substrate hydroxyphosphopyruvic acid was 32.8 μM, and the apparent Km for NADH 4.8 μM similar to the Kms for other mammalian 3 PGDHs. Enzyme activity was not altered by parenteral corticosteroids, a high carbohydrate diet, low protein diet, or starvation. Enzyme activity decreased over the first 12 days of life in newborn rats. The phosphorylated pathway of serine synthesis provides a potential nondietary and nonhepatic source for serine, glycine, and their products in keratinizing tissues.