Nicotinic acid (anionic form: nicotinate) is also known as niacin or vitamin B3. Nicotinamide is the amide derivative of nicotinic acid. Nicotinate and nicotinamide are essential for organisms as the precursors for generation of coenzymes, NAD+ and NADP+, which are essential for redox reactions and carry electrons from one reaction to another. They therefore exist in oxidised (NAD(P)+) and reduced (NAD(P)H) forms. These coenzymes are crucial for many metabolic pathways including glycolysis, TCA cycle, pentose phosphate cycle, fatty acid biosynthesis and metabolism pathways and many others. The apicomplexans such as Plasmodium falciparum and Toxoplasma gondii cannot synthesise nicotinate and nicotinamide de novo, but, they can salvage it from host or extracellular medium. These organisms can incorporate salvaged vitamin B3 derivatives to synthesise NAD+ and NADP+. In contrast, Cryptosporidium species do not possess the genes for the enzymes catalysing synthesis of NAD+ from nicotinate and nicotinamide. They possess NAD+ kinase and pyridine nucleotide transhydrogenase enzymes suggesting that they salvage NAD+ from host and convert them to NADP+.
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