Reports of feedback inhibition, regulatory subunits, allostericsites, and multi-protein complexes abound in the literature and it
remains a subject of active investigation. Active sites are regulated by three main allosteric bindings i) non-covalently of functional proteins to other proteins such as activators and repressors; ii) of metabolites, cyclic nucleotides, GTP37 and other small molecules non-covalently to catalytic or regulatory proteins; iii) covalent attachment of phosphate-, methyl-, acetyl-, etc.