tations, while those with inorganic electron acceptors (except 0 2 ) are described as anaerobic respiration. Respiration occurs when oxygen acts as the terminal oxidant. Terms such as "fumarate respiration" and "inorganic fermentation" are incompatible with this view.
A self-consistent definition of the basic metabolic types, i. e. fermentation, respiration, and photosynthesis, is provided by the relation of electron donor and acceptor systems on the one hand and the ATP* synthesizing pathways on the other (Table ). In fermentations, ATP* is formed by substrate level phosphorylation only, whereas cell respiration is a redox process in which ATP* is synthesized mainly by electron transport phosphorylation. Photosynthesis is dominated by light-driven electron transport phosphorylations.
COMMUNICATIONS
Inorganic fermentafion would thus be a redox process with a n inorganic electron acceptor, in which ATP* is formed exclusively by substrate level phosphorylation. Anaerobic respiration is an oxygen-free energy metabolism with an ATP* synthesis coupled to electron transport.
A consistent and functionally logical definition is obtained by assigning respiration to electron transport phosphorylation and fermentation to substrate level phosphorylation. The terms organic and inorganic fermentation and aerobic and anaerobic respiration then become unambiguous.