A comment on Warburg's early understanding of biocatalysis.

The early history of biochemistry was characterized by changing moods. The discovery of cell free fermentation (1897) led to the optimistic belief that all life processes were carried out by intracellular enzymes, being definite proteins with special catalytic properties. But, the persistent failure to isolate pure enzymes raised doubts. When Otto Warburg found cell respiration to be a membrane-bound iron catalysis (1914), he renewed the old position that biocatalysis was caused by surface forces and ferments could be heavy metal ions adsorbed on colloidal membrane carriers. This alternative view became popular when Warburg started his research in photosynthesis and explained his peculiar "photolyte" model. Neither the suggestion of surface-active colloidal ferments, nor the idea of "photolyte" stood the test of time and have now been rejected, but their history is of importance to how concepts evolve and die.