What is Cystatin C ?

Human Cystatin C, also named gamma-trace Protein or post-gamma-Globulin, is a basic inhibitor of cysteine proteases with a molecular mass of 13359 daltons.
It is produced at a constant rate in all nucleated cells and appears in human plasma and serum.

The cystatin superfamility of inhibitors of papain-like cysteine proteases

The amino acid sequences of human Cystatin C was determined in 1981. Then, it became evident that it belonged to a new superfamily which now contains 11 members of which Cystatin C is the most well characterized one.