Types of metabolic effects produced by analogues of vitamin-like substances

Evidence connecting the action of an analogue with its parent growth factor is of three main types. I.Antagonism in action This can be the clearest of all types of evidence; it has been much discussed, classified, and subjected to mathematical expression. For that reason I will say most about other types of evidence, and make only two observations concerning this first category, (a ) The antagonism can be observed at various levels: that of an overall biological effect such as growth, or at that of an individual enzymic.