Elementary plant Biochemistry and Biotechnology (2+1)

Niacin

• The coenzyme forms of niacin are NAD and NADP+ which function as the coenzymes of a large number of oxidoreductases collectively called as pyridine linked dehydrogenases.
• These coenzymes are bound to the dehydrogenase protein relatively loosely during the catalytic cycle and therefore serve as substrate than as prosthetic group.
  
• They function as electron acceptors during the enzymatic removal of hydrogen atoms from specific substrate molecules.
• One hydrogen atom from the substrate is transferred as a hydride ion to the nicotinamide portion of the oxidized forms of these coenzymes.
  
• The other hydrogen atom from the substrate becomes a hydrogen ion.
  
• Pyridine linked dehydrogenases are specific for either NAD+ or NADP+, but a few will function with both.
• Isocitrate dehydrogenase and lactate dehydrogenase are NAD-specific.
  
• Glucose 6-P dehydrogenase is NADP specific. Glutamate dehydrogenase functions with NAD + or NADP+.