The Era of Pathway Quantification

Biochemistry is in its third era, the Era of Quantification. So argues Koshland in his commentary, in which he describes this era as one in which the rates of production and degradation of substrates and products of biochemical pathways are quantified. In an example of this sort of analysis by Ferrel and Machleder in this issue, cell cycle regulation by the MAP kinase cascade is analyzed.