title: Enzyme kinetics studies on 29-kDa human liver cathepsin L.
abstract: Enzyme kinetics studies reported in the literature showed that human liver Cathepsin L is active only at lysosomal acidic pH values, while biochemical studies in living cells showed that the enzyme works even at neutral pH values (in a condition compatible with the extracellular compartment). Such an apparent ambiguity highlighted the need of analysing in depth the kinetics of ~29-kDa Cathepsin L, which is the form commonly used in experiments. The stability and catalytic activity of this enzyme were investigated at different pH values, reducing and non-reducing environments, presence of copper, iron and zinc ions, and presence of the natural modulator/inhibitor cystatin B. Our experiments showed that ~29-kDa human liver Cathepsin L is stable and catalytically functional even at neutral pH values and under non-reducing conditions, which simulate the extracellular compartment. Under these conditions, Cathepsin L was also proved to interact with cystatin B, being also modulated by physiological concentrations of Cu(++) , Fe(++) and Zn(++) . This paper suppose an advance in the comprehension of the catalytic properties of human liver Cathepsin L, its implications in different physiological processes and its potential use within a drug screening programme in which agents acting extracellularly are being considered.
authors.affiliation: Dipartimento di Farmacia, Università di Pisa, Via Bonanno 6, Pisa, 56126, Italy.
authors.forename: Daniele
authors.initials: D
authors.lastname: Pietra
authors.forename: Alice
authors.initials: A
authors.lastname: Borghini
authors.forename: Claudio
authors.initials: C
authors.lastname: Ricci
authors.forename: Anna M
authors.initials: AM
authors.lastname: Bianucci
mesh_terms: D055162:Biocatalysis; D056668:Cathepsin L / Q000737:chemistry / Q000378:metabolism*; D003300:Copper / Q000737:chemistry; D055313:Cystatin B / Q000737:chemistry / Q000378:metabolism; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007477:Ions / Q000737:chemistry; D007501:Iron / Q000737:chemistry; D007700:Kinetics; D008970:Molecular Weight; D013379:Substrate Specificity; D015032:Zinc / Q000737:chemistry
chemical_list: D007477:Ions; D003300:Copper; D055313:Cystatin B; D007501:Iron; D056668:Cathepsin L; D015032:Zinc
keywords: Cathepsin L; catalysis; cysteine protease; enzyme kinetics; enzyme progress curve