Effect of Various Inhibitors on Several Enzymes and Other Biochemical Substances in Chick Embryo Explants.

EARLIER studies in our laboratory indicated the predominance of pentose cycle In addition a correlation was demonstrated between enzymes generating reduced triphosphopyridine nucleotide and lipid synthesis (Bieber, Cheldelin & Newburgh, 1962; Baker & Newburgh, 1963). Since several of the biosynthetic pathways involve this compound, it is conceivable that in a rapidly growing system such as the early chick embryo enzymes generating TPNH may play a major role. We have chosen to use explants of chick embryos in an attempt to gain insight into the relation of changes of these enzymes with other chemical changes which may more directly relate to differentiation. These latter changes include synthesis of such macromolecules as DNA, RNA, hemoglobin, collagen and myosin. This method permits the addition of certain chemicals to the media such as substrates or inhibitors (Hayashi et ah, 1959), allowing easy manipulation of the environment. Prior to studying the above macromolecules it seemed appropriate to study the effect of certain inhibitors on glucoses-phosphate, 6-phosphogluconic acid and isocitric dehydrogenase. It was hoped that such information might be useful for purposes of establishing base lines of biochemical activity. The inhibitors chosen were fluorouracil, chloramphenicol and acetyl pyridine, and it will be shown that these had several rather specific effects on the enzymes studied. The first two inhibitors were chosen because of their relation to RNA or protein biosynthesis and the latter since it is an analogue of the pyridine moiety of TPN. In addition, Blackwood (1962) reported that chloramphenicol inhibited differentiation of the heart and ventral trunk if injected into eggs prior to Hamilton and Hamburger Stage 10 (1951). After this stage an inhibition of the