Biochemistry of Amino Acids - A. Meister 1961

The Role of Amino Acids in Nutrition
Amino Acid Antagonists
General Remarks

By altering The Structure of metabolite molecules, it is possible to obtain compounds that can no longer function normally in METABOLISM and thereby inhibit the Processing of their natural analogues. A classic example is the inhibition of succinate dehydrogenase activity by malonic acid [160]. In recent years, interest in antimetabolites has grown significantly, leading to the synthesis of numerous analogues of Amino Acids, Vitamins, Purines, and other metabolites. Some of these compounds are of considerable interest for biochemical research and therapeutic Applications [161–164]. The MECHANISM OF ACTION of antimetabolites is not yet fully understood, but it is known that they somehow impede the metabolism of their natural counterparts. Consequently, an antagonist can produce effects similar to those caused by a deficiency of the corresponding natural metabolic product. This inhibition can often be reversed by the simultaneous or prior administration of the natural metabolite. In other cases, the inhibition is more difficult to overcome or is completely irreversible. Under true competitive inhibition, The Effect of the inhibitor is proportional to The ratio of its concentration to that of the natural metabolite, with this proportionality holding across a wide range of concentrations. Not all analogues of natural metabolic products act as active antagonists; certain compounds exhibiting antagonistic effects in some biological systems may prove inactive in others. At the same time, a given analogue frequently shows activity across entirely distinct organisms. The correlations between specific molecular structural features and antagonistic activity have not yet been precisely established. Clarifying this issue requires further research using isolated enzyme systems. An approach to solving this problem is exemplified by the work of Neurath and co-workers, who extensively investigated inhibitors of certain Proteolytic Enzymes. Their findings provided valuable insights into the size and Nature of the active sites of these enzymes [165].

Halvorson and Spiegelman [166] conducted an interesting series of studies on substrate-induced enzyme formation in Yeasts. They examined the effects of numerous Amino Acid Antagonists on enzyme synthesis in the absence of exogenous nitrogen sources. The presence of a given antagonist prevented the incorporation of its homologue and also suppressed the utilization of all Other Amino Acids, revealing a direct correlation between growth inhibition and the suppression of enzyme formation. These findings align with other studies demonstrating that the simultaneous presence of all amino acids is required for Protein Synthesis [22, 75, 76].

When examining amino acid analogues, one is immediately struck by the close structural similarity among many Natural Amino Acids. Numerous Examples of antagonistic relationships exist between pairs of natural amino acids, and this picture becomes significantly more complex in systems containing multiple amino acids. Below are some of the simplest interactions between metabolites and antimetabolites among amino acids described in the literature. A Summary of the available data is presented in Table 17, which lists natural amino acids alongside their structural analogues tested as antimetabolites. Various biological systems were used to study this antagonistic activity. In most cases, the effect of antimetabolites on growth rate was investigated, alongside various in vitro experiments. Definitive Answers regarding the precise mechanism of antimetabolite action will likely come from studies on isolated enzyme systems.

Class="center">Table 17. Amino acid antagonists