Biochemistry - The Chemical Reactions of Living Cells, Volume 2 - D. Metzler 1980

Enzymes: Protein Catalysts of Cells
Regulation of Enzymatic Activity
Species Differences in Regulatory Mechanisms

During the course of evolution, the Catalytic Mechanism of certain Enzymes has remained unchanged, and protein molecules contain A number of invariant amino acid residues. However, The sequence of amino acid residues located On the surface of protein molecules can vary significantly from species to species. Since altering The Nature of the protein surface substantially affects its sensitivity to a potential allosteric effector, it is hardly surprising that the same enzyme isolated from different organisms often exhibits different regulatory properties. Thus, having labored to determine the regulatory mechanism for an enzyme isolated from one Organism, a biochemist often finds that it does not apply to the enzyme from another organism. While this circumstance greatly complicates the elucidation of metabolic pathways, it is of immense practical value. Differences in METABOLISM among species account for variations in the sensitivity of key organismal enzymes to poisons, drugs, and environmental pollutants. Bearing all this in mind, extreme caution must be exercised when extrapolating data obtained from animals to humans.