Chemistry and Biology of Proteins - F. Haurowitz 1953

Proteins with Hormonal Activity
General Data

Hormones produced by Endocrine glands are secreted directly into the bloodstream, which delivers them to their sites of action. Over the past few years, the chemical structures of sterol-derived hormones have been elucidated, whereas the formula of adrenaline—the hormone of The adrenal medulla—has been known for quite some time. While these hormones are compounds of relatively low molecular weight, the Hormones of the thyroid, parathyroid, and Pancreas, as well as those of the Pituitary Gland, are Proteins or protein derivatives with high molecular weights. They differ from low-molecular-weight hormones not only in molecular size, but also in their thermolability and MECHANISM OF ACTION. Investigations into The Structure of these hormones, isolated using standard Methods of Protein chemistry, have shown that they are built from well-known Amino Acids. To date, however, it has not been possible to determine precisely which molecular groups are responsible for the high physiological activity of these hormones. The situation in this field mirrors that of hydrolytic Enzymes, regarding the structure of whose functional groups we also know very little, despite numerous recent theories proposed to explain the Mechanism of Enzymatic action. In hormone chemistry, the state of affairs is even less satisfactory, as we lack even the basis to put forward a reasonably sound theory regarding their mechanism of action and must limit ourselves to a mere description of their properties. In the subsequent Discussion, special attention will be paid to those properties that distinguish individual hormones from one another, and the entire group of protein hormones from other proteins.

The following sections of this chapter will focus exclusively on protein hormones. One of the primary questions to address is whether protein hormones exhibit species Specificity. The species specificity of proteins is typically investigated immunologically by their ability to elicit antibody formation. Such studies have demonstrated that certain of these hormones, such as the pituitary gonadotropic hormone or the thyroid hormone, do indeed stimulate antibody production when parenterally injected into animals of another species. These Antibodies are sometimes referred to as antihormones [1–3], and their generation is precisely what is held responsible for the decline in hormonal activity observed during prolonged hormone administration [4]. Antibodies appear to be produced exclusively in response to the administration of high-molecular-weight hormones. Low-molecular-weight peptide-like hormones lack antigenic properties, and consequently, most of them retain their efficacy when administered to animals of another species, even over extended periods of time.