CO9, or Phosphoserine phosphatase pseudogene 1, is a human gene encoded by PSPHP1. It may also be known as: Putative phosphoserine phosphatase-like protein; L-3-phosphoserine-phosphatase homolog; PSPHL. The encoded protein has an amino acid length of 72 and a mass of 7.8 kDa. Other isoforms may exist. CO9 is a member of the SerB family.