Specific catalytic activity of cathepsin S in comparison to cathepsins B and L along the rat nephron.
Assay conditions were elaborated to determine the catalytic activity of cathepsin S fluorometrically for direct comparison with the activities of cathepsins B + L(+S) and B along the nephron of the normal rat. These conditions include the use of 0.5 mM Z-Phe-Arg-AMC as substrate, which is saturating for the three enzymes. The stability of cathepsin S at pH 7.5 and the resistance of cathepsin B against inactivation by 0.5 microM Z-Phe-Phe-CHN2 permitted differentiation of these enzyme activities. The catalytic activity of cathepsin S in rat kidney homogenate (1.11 mumol/min x g protein) amounted to 2.1% of that of cathepsins B + L(+S) and to 3.2% of that of cathepsin B. It was ten-fold higher in the cortex (1.54 mumol/min x g protein) than in the medulla resembling the activity ratio of cathepsins B + L(+S) and B. In suspensions of isolated glomeruli and isolated proximal tubules the activities of cathepsin S were 0.76 and 3.21 mumol/min x g protein, respectively. The corresponding activities of cathepsins B + L(+S) amounted to 80.0 and 211.7 mumol/min x g protein consisting of 71% cathepsin B activity. In nephron segments microdissected from lyophilized renal sections, highest cathepsin S activity was found in the proximal convoluted tubules (4.21 mumol/min x g dry weight) followed by 0.83 mumol/min x g dry weight in proximal straight tubules of the superficial cortex. In the remaining segments cathepsin S activity was hardly detectable. Unlike cathepsin S activity, the activity of cathepsin B was distributed in parallel to that of cathepsins B + L(+S). The presence of relatively high cathepsin S activity in proximal convoluted tubules in co-localization with the activities of cathepsins B + L(+S) and B suggests a primary role of these enzymes in heterophagocytosis of proteins from the ultrafiltrate.
Schmid
H
H
Institute of Pathology, University of Tübingen, Germany.
Koop
M
M
Utermann
S
S
Lambacher
L
L
Mayer
P
P
Schaefer
L
L
D000818:Animals; D002384:Catalysis; D002403:Cathepsins / Q000378:metabolism* / Q000502:physiology; D004210:Dissection; D007678:Kidney Glomerulus / Q000201:enzymology; D007679:Kidney Medulla / Q000201:enzymology; D007687:Kidney Tubules, Proximal / Q000201:enzymology; D008297:Male; D009399:Nephrons / Q000201:enzymology* / Q000601:surgery; D051381:Rats; D017207:Rats, Sprague-Dawley; D012680:Sensitivity and Specificity
D002403:Cathepsins