In cells, COX-1 and COX-2 metabolize arachidonic acid to PGH2 which is then converted to PGE2 by any one of three isozymes, PTGES, PTGES2, and PTGES3 or, alternatively, to PGD2 by either of two enzymes, a glutathione-independent synthase termed lipocalin-type Prostaglandin D2 synthase (PTGDS or L-PGDS) and a glutathione-dependent hematopoietic-type H-PGDS or PTGDS2; the COX's also metabolizes dihomo-gamma-linolenic acid to PGH1 which is metabolized by one of the three PTGES isomzymes to PGE1 (see eicosanoid#Prostanoid pathways). PGE2, PGE1, and PGD2 undergo a dehydration reaction PGA2, PGA1, and PGJ2, respectively. PGD2 conversions form the most studied cyclopentenone PGs. These conversions are as follows: