Activation of the 20S proteasome of Xenopus oocytes by cardiolipin: blockage of the activation of trypsin-like activity by the substrate.
The effects of an activator, cardiolipin, on the three peptidase activities of the 20S proteasome of Xenopus oocytes were examined. The trypsin-like activity was activated when the enzyme was treated with cardiolipin before the addition of the substrate, but there was no appreciable activation when cardiolipin was added concomitantly with the substrate. On the other hand, the chymotrypsin-like peptidase and peptidylglutamylpeptide hydrolase (PGPH) were activated regardless of the sequence of addition. When very low concentrations of the substrate (e.g. 0.1-0.5 microM; about 1/100 of the K(m)) were used, cardiolipin strongly activated trypsin-like peptidase by the simultaneous addition but not after substrate addition. These results suggest that the trypsin-type substrate produces a conformational change in the enzyme in a concentration-dependent manner which makes the activator sites inaccessible to cardiolipin.
Department of Biology and Geosciences, Faculty of Science, Shizuoka University, Japan. sbsyama@sci.shizuoka.ac.jp
S
S
Yamada
K
K
Sato
M
M
Uritani
T
T
Tokumoto
K
K
Ishikawa
D000818:Animals; D002308:Cardiolipins / Q000494:pharmacology*; D010450:Endopeptidases / Q000378:metabolism*; D004789:Enzyme Activation; D009097:Multienzyme Complexes / Q000378:metabolism*; D009865:Oocytes / Q000187:drug effects / Q000201:enzymology; D013379:Substrate Specificity; D014357:Trypsin / Q000378:metabolism*; D014982:Xenopus laevis
D002308:Cardiolipins; D009097:Multienzyme Complexes; D010450:Endopeptidases; D014357:Trypsin; C114177:peptidylglutamylpeptide hydrolase