Assay of α-Cysteine Proteinase Inhibitor in Serum or Plasma

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Abstract
A new proteinase inhibitor was recently found in human serum or plasma which specifically inhibits cysteine proteinases such as ficin, papain, bromelain and cathepsin B. However, serum contains .alpha.2-macroglobulin which also inhibits these cysteine proteinases and, consequently, interferes with the assay of the new .alpha.-cysteine proteinase inhibitor. Therefore, assay of the inhibitor in serum has not been established previously. The .alpha.2-macroglobulin is inactivated by preincubating the serum in methylamine solution at 55.degree. C, while the .alpha.-cysteine proteinase inhibitor retains its activity. The inhibitory power against cysteine proteinases is due mainly to this protein in human serum. This inhibitor is also found in mammals such as cows, pigs and rats. Vitamin E deficient rats show a very high inhibitor level. Therefore, this method will enable investigations of the relation between diseases and the activity of the .alpha.-cysteine proteinase inhibitor. Also, this method is simple and inexpensive. The necessary amount of serum is only 10 .mu.l.

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