Catalytic properties of human Lys77-plasmin. A comparative steady-state and pre-steady-state study

Paolo Ascenzi, Antonio Torroni, Enea Menegatti, Mario Guarneri, Gino Amiconi

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Values of kinetic parameters for the hydrolysis of esters and p-nitroanilides of l-lysine and l-arginine catalyzed by the Lys77 form of human plasmin (EC have been determined between pH 5.5 and 8 (I = 0.1 M) at 21 ± 0.5°C. Over the whole pH range explored, Lys77-plasmin catalysis conforms to simple Michaelis-Menten kinetics, and steady-state and pre-steady-state data may be consistently fitted to the minimum three-step mechanism: E+S⇌( k+1 k-1)E·S→(k+2)E·P+P1 →(k+3)E+P2 In spite of the higher specificity of lysyl derivatives for Lys77-plasmin rather than the arginyl ones, kinetic parameters also depend on the nature of the N-α substituent and/or of the alcoholic or p-nitroanilidic moiety of the substrate. Among the esters and anilides considered, ZLysONp shows the most favourable kinetic parameters and may be the substrate of choice of Lys77-plasmin, in that it allows the determination of the enzyme concentration as low as 2 × 10-9 M (about 1 × 10-3 CU/ml), at the optimum pH value (approx. 8). Between pH 5.5 and 8, the pH profiles of kcat and kcat/Km for the Lys77-plasmin-catalyzed hydrolysis of ZLysONp and ZArgONp reflect the ionization of a single group (probably His-602 involved in the active site) with pKa values ranging between 6.4 and 6.6; at variance, values of Km are pH-independent.

Original languageEnglish
Pages (from-to)215-219
Number of pages5
JournalBiochimica et Biophysica Acta (BBA)/Protein Structure and Molecular
Issue number2
Publication statusPublished - Nov 29 1985


  • (Human plasma)
  • pH effect
  • Plasmin
  • Proteinase kinetics
  • Substrate specificity

ASJC Scopus subject areas

  • Biochemistry
  • Biophysics
  • Molecular Biology
  • Structural Biology


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