INTRACELLULAR PROTEIN BREAKDOWN .7. CATHEPSIN L AND H - 2 NEW PROTEINASES FROM RAT-LIVER LYSOSOMES

  • 1 January 1976
    • journal article
    • research article
    • Vol. 35  (3-4) , 285-299
Abstract
Some properties of 2 previously unknown cathepsins from rat liver lysosomes are compared with the properties of the known cathepsin B1. Cathepsin L, a thiolproteinase, has a MW of 23-24,000 and a pI [isoelectric point] of 5.8-6.1. Disc electrophoresis and isoelectric focusing show 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 glutathione and EDTA in liquid N2 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 MW of 28,000 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.