After discussing what the hormone did, how to test for it, and its chemical nature, Williams reported on the manner in which the hormone acted; it directs the formation of an enzyme known as cytochrome.
All air-breathing animals, including humans, have cytochrome systems (a gourd of three iron-containing enzymes related to hemoglobin) in their body cells. These systems provide the basic means by which all animals utilize oxygen in the tissue.
In insects, Williams, and Howard Schneiderman found that the cytochrome enzymes are not synthesized unless the prothoracic hormone is present and that growth and differentiation is absolutely dependent on the function of the cytochrome system. In the absence of the hormone there is no cytochrome, and in the absence of the cytochrome, there is no growth.
Since this enzyme system occurs in all animals, and since in insects in controls growth, it seems likely that it also plays a crucial role in the growth of all animals.
Blocking the System
In the last section of his address, Williams said that there were three proofs of this theory of cytochrome controlled growth. The basic idea in all was to use various agents to block the cytochrome system selectively, that is, to affect the cytochrome system without harming the other parts of the animal.
It was found that high pressures of carbon monoxide will block the action of cytochrome, by combining with it and forming a combination compound which does not have the power to handle oxygen.
The blocking by CO is reversed by light. By pinpointing light on a particular areas, growth was immediately resumed in that area, while the unilluminated parts continued to lie dormant.
Another way to block the cytochrome is to use purified diphtheria toxin. Diphtheria toxin is a protein excreted by diphtheria bacilli, and is a part of the bacterium's cytochrome b, which in turn is an enzyme in that bacterium's cytochrome system.
The diphtheria toxin a cytochrome enzyme, gets into the human body and is mistakenly incorporated into its cytochrome system--the cytochromes of all animals are related but not identical.
The human cytochrome can't function properly, and since no oxygen can then be utilized, there is no growth. When this happens, the human dies.
Proof Positive?
Proof of this theory was again found in insects. At the non-growing stage when the cytochrome system is absent (the pupal stage), the insect was found to be wholly resistant to diphtheria toxin. But at other stages, when cytochrome is present, the toxin caused an immediate cessation of growth and ultimately caused death.
Imidazole and certain other organic chemicals attack the cytochrome in a third way. These chemicals combine with all the available sources of iron and thus prevent the formation of cytochrome. This block also causes the immediate cessation of growth.
These studies have therefore demonstrated several ways in which the growth mechanism can be disassociated from the maintenance mechanism by he action of chemicals whose biochemical target within the living cell is the cytochrome system.
Significance to Cancer
Such chemicals appear to be of great interest since they may lead to suitable non-toxic substance to block malignant growth.
Williams is interested in normal growth, because "the understanding of normal growth mechanisms is necessary for the rational understanding of that aberration of the normal process which produces malignant diseases such as tumors and cancers.
He adds that "When we completely understand the normal growth mechanisms and its hormonal control, then we will have the basic facts for understanding the abnormal, since the problem of hormones is right at the center of the cancer problem.