53 catalytic interaction between enzyme-coenzyme complex and substrate (VENNESLAND and WESTHEIMER 1954; VENNESLAND 1955,1956; GUTFREUND 1959) have all been the subject of numerous excellent and exhaustive reviews. These topics, therefore, will not be treated in extenso here. The present summary will deal instead with more recent observations on the pyridine nucleotide dependent dehydrogenases which have necessitated a re-examination of their function and structure in the light of new information concerning their composition. The new compositional characterization of these enzymes dates from...