A zinc-binding enzyme belonging to the family of high molecular weight metalloproteinases. In addition to being synthesised in the placenta, plasma protein A is present in a wide range of reproductive (e.g. testis and endometrium) and non-reproductive (e.g. kidney and colon) tissues and organs, but at much lower concentrations than during pregnancy. It is also known as pregnancy-associated plasma protein-A (PAPP-A).