Elsevier

Biochemical Pharmacology

Volume 22, Issue 23, 1 December 1973, Pages 3099-3108
Biochemical Pharmacology

Relationship between the inhibition constant (KI) and the concentration of inhibitor which causes 50 per cent inhibition (I50) of an enzymatic reaction

https://doi.org/10.1016/0006-2952(73)90196-2Get rights and content

Abstract

A theoretical analysis has been made of the relationship between the inhibition constant (KI) of a substance and the (I50) value which expresses the concentration of inhibitor required to produce 50 per cent inhibition of an enzymic reaction at a specific substrate concentration. A comparison has been made of the relationships between KI and I50 for monosubstrate reactions when noncompetitive or uncompetitive inhibition kinetics apply, as well as for bisubstrate reactions under conditions of competitive, noncompetitive and uncompetitive inhibition kinetics. Precautions have been indicated against the indiscriminate use of I50 values in agreement with the admonitions previously described in the literature. The analysis described shows KI does not equal I50 when competitive inhibition kinetics apply; however, KI is equal to I50 under conditions of either noncompetitive or uncompetitive kinetics.

References (9)

  • S. Cha

    J. biol. Chem.

    (1968)
  • P. Voytek et al.

    J. biol. Chem.

    (1972)
  • W.W. Cleland

    Biochim. biophys. Acta

    (1963)
  • W.W. Cleland

    Biochim. biophys. Acta

    (1963)
There are more references available in the full text version of this article.

Cited by (12793)

View all citing articles on Scopus

This research was supported by United States Public Health Research Grant CA-05262.

View full text