Flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD) are the two coenzyme forms of riboflavin. The ribitol (5-arbon) is linked to a phosphate in FMN. FAD is formed from FMN by transfer of an AMP moiety from ATP.
The nucleotide coenzymes FMN, FAD, NAD+, NADP+, and coenzyme-A are synthesised from the B-complex vitamins.
INTRODUCTION The protein of 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 for catalysis. Coenzymes are second substrates and are often regarded as co-substrates. Coenzymes undergo alterations during the enzymatic reactions, which are…
Reaction 12 (Refer Figure 11.7) is the sole reaction of pyrimidine nucleotide biosynthesis, which requires a tetrahydrofolate derivative. During the transfer process, the methylene group of N5 and N10 methylene THF is reduced to a methyl group, and the tetra hydrofolate carrier oxidised to dihydrofolate must be reduced to tetrahydrofolate in a reaction catalysed by tetrahydrofolate reductase. Consequently, dividing…
The pyrimidine nucleotides undergo similar reaction (dephosphorylation, deamination, and cleavage of glycosidic bond) like that of purine nucleotides to liberate the nitrogenous bases cytosine, uracil, and thymine. The bases are then degraded to highly soluble products β-alanine and β-aminoisobutyrate and other reactions to finally produce acetyl CoA and succinyl CoA. The degradation of pyrimidine nucleotides…
The first two enzymes of pyrimidine nucleotides biosynthesis is sensitive to allosteric regulation with respect to the regulation of gene expression. The first three and the last two enzymes of the pathway are regulated by apparently coordinate repression and depression. Carbamoyl phosphate synthase is inhibited by UTP and purine nucleotides but is activated by PRPP.…
Mammalian cells lack efficient means of salvaging pathway for pyrimidine bases. Salvage reactions convert the pyrimidine ribonucleotides uridine and cytidine and the deoxyribonucleosides thymidine and deoxycytidine to their respective nucleotides. Deoxycytidine is phosphorylated by deoxycytidine kinase, an enzyme that also phosphorylates deoxyguanosine and deoxyadenosine. Orotate phosphoribosyl transferase, an enzyme of de novo synthesis of pyrimidine…
Pyrimidine ring is first synthesised and then attached to ribose 5-phosphate. This is in contrast to purine nucleotide synthesis, where in purine, the ring is built upon a preexisting ribose 5-phosphate. Glutamine transfers its amido nitrogen to CO2 to produce carbamoyl phosphate. This reaction is ATP dependent and is catalysed by cytosol enzyme carbamoyl phosphate synthetase…
The synthesis of pyrimidine is a much simpler process compared to that of purines. Aspartate, glutamine (amide group), and CO2 contribute the atoms in the formation of pyrimidine ring.
Folic acid (THF) is essential for the synthesis of purine nucleotides (reactions 4 and 10)-Refer to Figure 11.2. Sulphonamides are the structural analogues of para aminobenzoic acid (PABA). These sulpha drugs can be used to inhibit the synthesis of folic acid by micro-organisms. This indirectly reduces the synthesis of purines and therefore the nucleic acids (DNA…