Question

1. Describe NADPH and the role of NADPH in metabolism.

Answer 1

Ans. NADPH stands for Nicotinamide Adenine Dinucleotide Phosphate (reduced form) is formed from reduction of NADP​​​+ . Synthesis of NADPH is done following either de-novo or salvage pathway wherein its synthesis starts from NAD+ mediated by the enzyme NAD+ kinase. The role of kinase enzyme is transfer of phosphate group. NADPH is produced in Pentose-phosphate pathway in the first step mediated by enzyme, Glucose-6-phosphate dehydrogenase in animals as well as other non-photosynthetic organisms. In case of photosynthetic organisms, NADPH is produced in majority from Ferredoxin-NADP+ reductase which is prevalent in all life forms. Its production is at the last step of light reaction in photosynthesis which in turn used for as energy source for carbon dioxide fixation to glucose during Calvin cycle. Role of NADPH in metabolism is prominent. NADPH can function as cofactor. It can donate electron and hydrogen to many enzyme catalytic reactions. Some large biomolecules are synthesized in the mitochondrial matrix by utilizing NADPH. NADPH can also act as coenzymes. For example, in case of enzyme adrenodoxin reductase,two electrons are transferred from NADPH to FAD for synthesis of steroid hormone. Majorly in anabolic pathways involving creation of large molecules there is utilization of NADPH. It is the energy carrier. NADPH is maintained at most of the time at higher concentration in the cytoplasm for enabling the synthesis of large biomolecules by reduction of small molecules easily. There is requirement of NADPH and ATP for the synthesis of fatty acids which is a reductive process. In anti-oxidative defence system there is requirement of NADPH as reducing agent and GSH is regenerated from GSSH by using NADPH mediated by the enzyme glutathione reductase. Reduction of ribonucletides to deoxyribonucleotides by ribonucleotide reductase enzyme requires NADPH and hence it indirectly participates in DNA synthesis. As such role of NADPH in DNA, which is the hereditary material, shows the importance of NADPH in existence of life.