Human Biochemistry, Volume 1 - Murray R. 1993

Structure and Functions of Proteins and Enzymes
Enzymes: Regulation of Activity
Biomedical Significance

The mechanisms by which Cells and whole organisms coordinate and regulate their entire array of metabolic processes are of great interest to researchers across a diverse range of biomedical fields. These include The Study of carcinogenesis, cardiovascular diseases, Aging, microbial physiology, Cell Differentiation, metamorphosis, and the Action of Hormones and drugs. All of these areas exhibit medically significant Examples of dysregulated enzyme function. For instance, studies on experimental tumors reveal that many Cancer cells display regulatory defects that alter the proportional synthesis of Enzymes, such as a failure of enzyme induction or repression. This Supports the well-established principle that a fundamental hallmark of cancer cells is a breakdown in Genetic control systems. As another example, certain Oncogenic Viruses carry a Gene encoding a Tyrosine protein kinase; when expressed in host cells, this kinase phosphorylates numerous Proteins and Enzymes that are normally unphosphorylated, leading to profound alterations in the cellular phenotype. Changes of this nature appear to underlie an entire category of cellular transformations induced by oncogenic viruses. Finally, in the aforementioned field of drug action, we encounter numerous examples highlighting Structure/19.html">The Importance of enzyme regulation. Specifically, the administration of certain drugs can stimulate the Synthesis of specific enzymes, acting as enzyme Inducers. For example, phenobarbital triggers a substantial 3- to 5-fold increase in the levels of the microsomal enzyme cytochrome P-450, which plays a pivotal role in the METABOLISM of phenobarbital itself and many other pharmacological agents. One such agent is warfarin, an anticoagulant. If a patient taking warfarin is subsequently prescribed phenobarbital, the warfarin dosage must be significantly increased to compensate for its accelerated degradation by the induced cytochrome P-450. Enzyme induction represents a major biochemical mechanism underlying drug-drug interactions, where the administration of one medication significantly alters the metabolism of another.