Enzymatic transamination consists of the enzyme catalyzed reversible transfer of the alpha amino nitrogen of an amino acid to an alpha-keto acid with the synthesis of a second amino acid and a second alpha-keto acid. Enzymes catalyzing different transamination reactions are found widely distributed in animal tissues and have been shown to change in activity in some tissues during disease (1-3). These observations prompted the present study to determine if transaminase activity could be demonstrated in human serum and blood cellular elements and, if so, to study any variations in activity of this enzyme in the blood of normal and diseased man.

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Transaminase activity in human blood

The mechanism of action of glucocorticoids is reviewed from the standpoint of seeing how far current concepts of the molecular action of steroids go towards explaining the varied physiologic and metabolic effects induced. The role of plasma binding to transport proteins in modifying steroid action is considered. The interactions between glucocorticoids and other hormones, particularly those mediated by cAMP are considered along with a discussion of the mechanism of “permissive” effects. Various proposals concerning the way in which glucocorticoids induce their effects including direct interactions with enzymes, nucleic acids, lysosomes, and receptor proteins are considered in detail, and an attempt is made to consider how far each of these mechanisms can go in explaining steroid action. Those biologic effects that cannot be accounted for by currently available mechansims are mentioned. Effects of glucocorticoids on growth, differentiation, and the inflammatory response are discussed from a mechanistic point of view. Catabolic or inhibitory effects of glucocorticoids as well as enzyme induction are examined using several exemplary systems. Finally an attempt is made to summarize the current state of knowledge concerning glucocorticoid and genome interaction.

Mechanism of action of glucocorticoids.

Evidence is accumulating that, in the brain, the amino–acids L-glutamate and γ-aminobutyric acid (GABA) are essential agents of communication and not just elements of an alternate metabolic pathway, as was generally believed for some years.

Glutamate and γ -Aminobutyric Acid in Brain

Publisher Summary This chapter examines some of these questions with respect to vitamin B6. The problem can be considered from three points of view: (1) what are the structural features required for vitamin B6 activity in living organisms, (2) what structural features determine the ability of a compound to serve as a coenzyme for vitamin B6-dependent enzymes, and (3) apart from ability to combine with its conjugate apoenzymes, what chemical features determine the ability of the coenzyme to participate in catalysis of the reactions for which it is essential? These questions can be profitably considered in reverse order because unless the chemical prerequisites for participation in catalysis are present, a compound obviously will be of no value as a coenzyme, however closely it may resemble the coenzyme in other respects. By the same token, it cannot serve as a vitamin, the sole function of which is to serve as a precursor for coenzyme formation.

Chemical structure in relation to biological activities of vitamin B6.

The scope of the transamination reaction in animal tissues.

Publisher Summary This chapter focuses on the role of transamination in amino acid and protein metabolism, with a minimum of purely enzymological information A rather extended discussion of the metabolic functions of dicarboxylic amino acids and their precursors is included to arrive at a clearer insight into the metabolic interrelations of transamination and its physiological significance, which are still imperfectly understood Deamination of amino acids by carbonyl compounds has long been known in organic chemistry Classical instances are the Strecker reaction of amino acids with alloxan and similar reactions with o-quinones, satin, ninhydrin, methylglyoxid, and the like The central position of the dicarboxylic acid system in tissue metabolism is clearly demonstrated by the role of its components in respiratory hydrogen transport, in aerobic phosphorylation, in the formation, interconversion and breakdown of amino acids, in the fixation and liberation of carbon dioxide and of ammonia, in the synthesis of specific nitrogenous cell substances and end products The designation of this system as a central component of first order in the chemical integration of nitrogenous metabolism is, therefore, fully justified This conception satisfactorily accounts for the widespread occurrence of transamination and for its exceptionally high activity in certain tissues

Alexander E. Braunstein

Papers

Transamination and the integrative functions of the dicarboxylic acids in nitrogen metabolism.