Regulation of the activity of lysosomal cysteine proteinases by pH-induced inactivation and/or endogenous protein inhibitors, cystatins.
The kinetics of pH-induced inactivation of human cathepsins B and L was studied by conventional and stopped-flow methods. The inactivation of both enzymes was found to be an irreversible, first-order process. The inactivation rate constants increased exponentially with pH for both enzymes. From log kinac vs pH plots, 3.0 and 1.7 protons were calculated to be desorbed for pH-induced inactivation of cathepsins L and B. Cathepsin B was thus substantially more stable than cathepsin L (approximately 15-fold at pH 7.0 and 37 degrees C). Cathepsin B was efficiently inhibited by cystatin C at pH 7.4, whereas the inhibition by stefin B and high molecular weight kininogen was only moderate. In contrast, cathepsin L was efficiently inhibited by both chicken cystatin and stefin B at this pH kass approximately 3.3 x 10(7) m-1 s-1).
Turk
B
B
Dept. Biochemistry and Molecular Biology, J. Stefan Institute, Ljubljana, Slovenia.
Bieth
J G
JG
Björk
I
I
Dolenc
I
I
Turk
D
D
Cimerman
N
N
Kos
J
J
Colic
A
A
Stoka
V
V
Turk
V
V
D000818:Animals; D002401:Cathepsin B / Q000037:antagonists & inhibitors; D056668:Cathepsin L; D002403:Cathepsins / Q000037:antagonists & inhibitors; D002645:Chickens; D015891:Cystatins / Q000502:physiology*; D003546:Cysteine Endopeptidases / Q000378:metabolism*; D010450:Endopeptidases; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008247:Lysosomes / Q000201:enzymology*
D015891:Cystatins; D002403:Cathepsins; D010450:Endopeptidases; D003546:Cysteine Endopeptidases; D002401:Cathepsin B; C534281:CTSL protein, human; D056668:Cathepsin L; C028217:cathepsin S