[Intracellular protein breakdown. VII. Cathepsin L and H; two new proteinases from rat liver lysosomes].
Some properties (molecular weight, pI, temperature stability, action of selected inhibitors, substrate specificity and pH-activity dependence) of two not yet known cathepsins from rat liver lysosomes are compared with the properties of the known cathepsin B1. Cathepsin L is a thiolproteinase, has a molecular weight of 23--24000 and a pI of 5,8--6,1. By disc electrophoresis and isoelectric focusing there appear several protein bands which all have enzymatic activity. Leupeptin behaves as a strong inhibitor. The pH-optimum for digestion of proteins is close to 5,0. Cathepsin L does not hydrolyse esters and splits synthetic low molecular substrates only to a low degree. Cathepsin L stored in presence of glutathion and EDTA in liquid nitrogen kept its activity for some months. Cathepsin H is an aminopeptidase as well as an endopeptidase. An enzyme with these bifunctional properties was detected up to now only in E. coli but not in animal cells. Cathepsin H is a thiol-enzyme with a molecular weight of 28000 and a pI of 7,1. Strong inhibitors are leucyl-chlormethan and SH-blocking substances. Leupeptin shows only a weak inhibitory effect to this enzyme compared to its action on cathepsins L and B1. The pH-optimum for hydrolysis of all substrates is 6.0. Cathepsin H splits proteins, amino acid derivatives and selected N-protected amino acid derivatives. Cathepsin H compared to cathepsin L and B1 is quite temperature stable.
D000818:Animals; D002403:Cathepsins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D004355:Drug Stability; D006863:Hydrogen-Ion Concentration; D007526:Isoelectric Point; D007527:Isoenzymes / Q000378:metabolism; D007700:Kinetics; D008099:Liver / Q000201:enzymology*; D008247:Lysosomes / Q000201:enzymology*; D008970:Molecular Weight; D051381:Rats
D007527:Isoenzymes; D002403:Cathepsins
Intrazellulärer Proteinabbau. VII. Kathepsin L und H: Zwei neue Proteinasen aus Rattenleberlysosomen