Covalent modification of proteins as a threshold mechanism in development

J Theor Biol. 1990 Jan 23;142(2):243-50. doi: 10.1016/s0022-5193(05)80225-5.


Thresholds are a central but somewhat neglected aspect of cellular processes in development. An analysis has been made of the conditions in which different thresholds can be generated in the covalent modification of a number of target proteins when the concentration of an effector is continuously increased. It is assumed that the effector, which could represent a morphogen, activates, for example, kinases that phosphorylate the proteins. Thresholds are found when the modifying enzymes are saturated by their protein substrates, i.e. in conditions of zero-order ultrasensitivity (Goldbeter, A. & Koshland, D. E. 1981. An amplified sensitivity arising from covalent modification in biological systems. Proc. natn. Acad. Sci. U.S.A. 78, 6840-6844). Sequential thresholds can be generated when the kinase/phosphatase pairs differ either in the ratio of maximum modification rates or in the affinity of the effector for each kinase.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Enzyme Activation / physiology*
  • Models, Biological
  • Phosphorylation
  • Phosphotransferases / metabolism
  • Proteins / physiology*


  • Proteins
  • Phosphotransferases