Kallikrein 9, also known as Kallikrein-Like 3 (KLK-L3), is a chymotrypsin-like serine proteinase. Kallikrein 9 was discovered as the locus for kallikreins on chromosome 19 was more fully mapped and found by similarity to the other tissue kallikreins. Kallikrein 9 has been found in the ovary, thymus, testis, prostate, skin, breast and neuronal tissues and is made by many cell lines in culture. Kallikrein 9 levels in breast cancer and uterine cancer patients have been reported to drop as the disease progresses, thus hK9 might be considered a favorable prognostic marker. Different splice variants of hK9 have been reported, although it is not yet known if they produce functional proteins. The full length Kallikrein 9 encodes for a 250 amino acid protein, with a predicted mass of 27.5 kDa and a pI of 7.53. The 234 amino acid form predicts a protein of 26 kDa with a pI of 9.76 and this quite basic pI might give the shorter form a very different function or localization. The shorter sequence also diverges before the catalytic serine residue, making it unlikely to be proteolytically active. Pre-pro-kallikrein 9 has the 17 amino acid signal sequence is removed before secretion, and the Pro-kallikrein 9 is activated to Kallikrein 9 by removal of the 5 amino acid propeptide domain.