GGH is a 318 amino acid protein that is secreted into the extracellular space and is also localized to both the lysosome and the melanosome. Functioning as a hydrolase, GGH contains one gamma-glutamyl hydrolase domain through which it catalyzes the hydrolysis of polyglutamate sidechains from pteroylpolyglutamates, specifically hydrolyzing gamma-glutamyl bonds. Via its catalytic activity, GGH may play a role in the bioavailability and metabolic activity of pteroylpolyglutamates. Polymorphisms