Some properties of human and bovine brain cathepsin B |
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Authors: | Anahit Azaryan Nina Barkhudaryan Armen Galoyan |
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Institution: | (1) Institute of Biochemistry, Armenian SSR Academy of Sciences, 375044 Yerevan, USSR |
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Abstract: | Cathespin B has been purified 750-fold to apparent homogeneity from human and bovine brain cortex using ammonium sulfate fractionation
(30–70%), chromatography on Sephadex G-100, CM-Sephadex C-50, and concanavalin A-Sepharose. Enzyme was assayed fluorometrically
at pH 4.0 with pyridoxyl-hemoglobin in the presence of 1 mM DTT and 1 mM EDTA. Properties of the enzyme from the two sources
proved to be similar. On disc PAGE the purified preparation produced two bands associated with proteinase activity that are
due to existence of two multiple forms of brain cathepsin B with pI 6.1 and 6.8. The enzyme is completely inactivated by thiol-blocking
reagents, leupeptin, E-64, and demands thiol compounds for its ultimate activity. Z-Phe-Ala-CHN2 is a potent inhibitor of the enzyme (K
2nd=1280 M−1s−1) in contrast to Z-Phe-Phe-CHN2 (K
2nd=264 M−1s−1). pH optimum in the reaction of hydrolysis of Pxy-Hb is 4.0–6.0,K
M(app.) =10−5 M. Cathepsin B splits azocasein: pH optimum 5.0–6.0,K
M(app.)=2.2·10−5 M, but inclusion of urea in the incubation medium depresses the azocaseinolytic activity of the enzyme 1.5-fold. It does
not split Lys-NNap, Arg-NMec and is not inhibited by bestatin. The specific activity of brain cathepsin B with Z-Arg-Arg-NNapOMe
at pH 6.0 is 10-fold higher than with Bz-Arg-NNap, Z-Gly-Gly-Arg-NNap is a poor substrate. With Z-Arg-Arg-NMec and Bz-Phe-Val-Arg-NMec
the specific acitivity is 80 and 35%, respectively of that with Z-Phe-Arg-NMec.
Special Issue dedicated to Dr. Eugene Kreps. |
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