HumanKine human Cystatin C is expressed as a non-glycosylated monomer in human HEK 293 cells. Cystatin C belongs to the cystatin superfamily. Two isoforms (pI = 7.8, 9.2) of native Cystatin C are found in human urine differentiated by the elimination of small basic peptides or amino acids from the N-terminal end of the protein. This protein is coded by a housekeeping gene, CST3 located on human chromosome 20p11.21 and is generated by nucleated cells.

Cystatin C human has been used as a standard in western blot assay. It has also been used to study its effect on the endopeptidase activity of activated Trichobilharzia regenti isoform of cathepsin B1 peptidase (TrCB1).

Cystatin C is an inhibitor of cysteine proteases including cathepsin B which has been identified as the most important β-amyloid-degrading enzyme. Measurement of cystatin C in serum is replacing creatinine as an indicator of kidney function (glomerular filtration rate, GFR). Studies show its role in predicting new-onset or deteriorating cardiovascular disease. It also seems to play a role in brain disorders involving amyloid, such as Alzheimer′s disease. Cystatin C inhibits transforming growth factor β signaling in normal and cancer cells.

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The inhibitory function of cystatin c on papain′s protease activity was measured by a colorimetric assay using L-BAPA as substrate. IC₅₀ value was measured at 5 to 20 μg/mL (0.3 to 1.5 μM) with a range of 1.56 μg/mL to 50 μg/mL cystatin C in presence of 0.55 μM papain and 0.44 μM L-BAPA.

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