PHYSICOCHEMICAL PROPERTIES OF BRAIN CATHEPSIN-H

Cathepsin H (EC 3.4.22.16) from cow brain, purified to similar to 1800 -fold with similar to 26% activity yield, hydrolysed BANA, Leu-2-NNap, Arg-2-NNap, and Met-2-NNap maximally at pH 6.5, 6.8, 7.0 and 7.2, res pectively. It was activated by sulphydryl compounds and EDTA while sul phydryl alkylators and blockers were found to inhibit the enzyme activ ity. Met-2-NNap was found to be the best substrate followed by Thr-2-N Nap, His-2-NNap, Leu-2-NNap, Arg-2-NNap and Ala-2-NNap, respectively. The K-m values for hydrolysis of various substrates viz., Met-2-NNap, Leu-2-NNap, Arg-2-NNap, Arg-NNapOMe, Thr-2-NNap, His-2-NNap, BANA, Arg -pNA and Lys-pNA were 0.128, 0.167, 0.169, 0.288, 0.428, 0.500, 0.667, 0.195 and 0.476 mM, respectively. The temperature optima for hydrolys is of BANA and Leu-2-NNap were similar to 45 degrees C and similar to 50 degrees C with activation energies of similar to 13.7 and similar t o 11.0 kcal mole(-1), respectively. The enzyme was fairly stable upto 50 degrees C and between pH 4.0-7.5.