Coenzymes participate in transfer of atoms or groups like hydrogen, aldehyde, keto, amino, acyl, methyl, carbon dioxide, and so on.
Coenzymes are often regarded as the second substrates or cosubstrates, since they have affinity with the enzymes comparable with that of the substrates. Coenzymes undergo alterations during the enzymatic reactions which are later regenerated. This is constant to the substrate which is converted to the product.
The protein part of the enzyme on its own is not always adequate to bring about the catalytic activity; many enzymes require certain non-protein small additional factors, collectively referred to as cofactors. The non-protein, organic, low molecular weight and dialysable substance associated with enzym
Cu, Zn, Mo, Fe, and Co cations. Transition metal ions bind to enzymes much more strongly than the metal ions and form metalloenzymes. Mo and Fe are found in nitricoxide reductase; Fe is a component of Hb, the carrying haemoprotein of erythrocytes. Co is found in vitamin B12. Superoxide dismutase is a copper-metalloenzyme, which catalyses the…
Oxygen atoms are often involved in the bonds of both alkali metal and alkaline earth metal cations, bonds of the latter being relatively stronger. Mg2+ is accumulated by cells in exchange for transport of Ca2+ in the opposite direction. So Ca++ activation enzymes are mostly extracellular ones. Example: Salivary and pancreatic α-amylases. Intracellular enzymes require Mg2+ for activity, and…
Alkali metal cations bind only weakly to form complexes with enzymes, but K+, the most abundant intracellular cation, is known to activate a great many enzymes, particularly those catalysing phosphoryl transfer or elimination reaction. It appears that K− is largely bound to be a negatively charged group on an inactive form of the enzyme and…
Metalloenzymes: Metal is tightly bound and retained by the enzyme for purification. Metal-activated enzyme: Binding is less tight, and purified enzymes may have to be activated by addition of metal ions.
Some of the enzymes require certain inorganic metallic cations like Mg2+, Mn2+, Zn2+, Ca2+, Co2+, Cu2+, Na+, K+, and so on, for their optimum activity. Rarely anions are also needed for enzyme activity (e.g. chloride ion Cl− for amylase). Two categories of enzymes requiring metals for their activity are distinguished: METAL-ACTIVATED ENZYMES AND METALLOENZYMES Almost ¼…
The catalytic activity of certain enzymes is reversibly altered by certain inorganic and organic molecules called modifiers or modulators or effectors. Those molecules which increase the enzyme activity are called positive modifiers or activators. And those which decrease the enzyme activity are called negative modifiers or inhibitors. Many metals act both as positive and negative…