The High Energy State

Abstract

In photosynthetic phosphorylation ATP synthesis is coupled to the redox reactions driven by light: this mechanism of coupling implies thermodynamically the existence of some common intermediate, generated by photosynthetic electron transport and able to store the energy to be utilized during the synthesis of ATP. The concept of high energy state (HES) is concerned with the nature and the properties of this “energized state” of phosphorylating membranes. Since the literature in this field, covering common aspects of respiration, photosynthesis and chemosynthesis, as well as aspects of the mechanism of active transport of metabolites, is very large, and since special topics in this area will be dealt with in other chapters of this book, the discussion will be limited here only to some important points: 1. current and historically important theories on the nature of the HES. 2. experimental evidence of the existence of an HES distinct from the immediate precursor of ATP. 3. experimental evaluation of the energy level and the energy capacity of the HES.