Nucleotides are organic molecules composed of a nitrogenous base, a pentose sugar and a phosphate. They serve as monomeric units of the nucleic acid polymers – deoxyribonucleic acid (DNA) and ribonucleic acid (RNA), both of which are essential biomolecules within all life-forms on Earth. Nucleotides are obtained in the diet and are also synthesized from common nutrients by the liver.
In biochemistry, a kinase is an enzyme that catalyzes the transfer of phosphate groups from high-energy, phosphate-donating molecules to specific substrates. This process is known as phosphorylation, where the high-energy ATP molecule donates a phosphate group to the substrate molecule. This transesterification produces a phosphorylated substrate and ADP. Conversely, it is referred to as dephosphorylation when the phosphorylated substrate donates a phosphate group and ADP gains a phosphate group. These two processes, phosphorylation and dephosphorylation, occur four times during glycolysis.
In molecular biology, biosynthesis is a multi-step, enzyme-catalyzed process where substrates are converted into more complex products in living organisms. In biosynthesis, simple compounds are modified, converted into other compounds, or joined to form macromolecules. This process often consists of metabolic pathways. Some of these biosynthetic pathways are located within a single cellular organelle, while others involve enzymes that are located within multiple cellular organelles. Examples of these biosynthetic pathways include the production of lipid membrane components and nucleotides. Biosynthesis is usually synonymous with anabolism.
GTP cyclohydrolase I (GTPCH) (EC 3.5.4.16) is a member of the GTP cyclohydrolase family of enzymes. GTPCH is part of the folate and biopterin biosynthesis pathways. It is responsible for the hydrolysis of guanosine triphosphate (GTP) to form 7,8-dihydroneopterin triphosphate (7,8-DHNP-3'-TP, 7,8-NH2-3'-TP).
GTP cyclohydrolases are enzymes that catalyze imidazole ring opening of guanosine triphosphate (GTP). This reaction is the committed step in the biosynthesis of multiple coenzymes, tRNA bases, and the phytotoxin toxoflavin. Several GTP cyclohydrolases exist, which sometimes synthesize different products for different pruposes:
Isopentenyl pyrophosphate isomerase, also known as Isopentenyl-diphosphate delta isomerase, is an isomerase that catalyzes the conversion of the relatively un-reactive isopentenyl pyrophosphate (IPP) to the more-reactive electrophile dimethylallyl pyrophosphate (DMAPP). This isomerization is a key step in the biosynthesis of isoprenoids through the mevalonate pathway and the MEP pathway.
Purine metabolism refers to the metabolic pathways to synthesize and break down purines that are present in many organisms.
GMP reductase EC 1.7.1.7 is an enzyme that catalyzes the irreversible and NADPH-dependent reductive deamination of GMP into IMP.
Riboflavin synthase is an enzyme that catalyzes the final reaction of riboflavin biosynthesis. It catalyzes the transfer of a four-carbon unit from one molecule of 6,7-dimethyl-8-ribityllumazine onto another, resulting in the synthesis of riboflavin and 5-amino-6-ribitylamino-2,4(1H,3H)-pyrimidinedione:
In molecular biology, the protein domain SAICAR synthase is an enzyme which catalyses a reaction to create SAICAR. In enzymology, this enzyme is also known as phosphoribosylaminoimidazolesuccinocarboxamide synthase. It is an enzyme that catalyzes the chemical reaction
In enzymology, a GTP cyclohydrolase IIa (EC 3.5.4.29) is an enzyme that catalyzes the chemical reaction
In enzymology, an IMP cyclohydrolase (EC 3.5.4.10) is an enzyme that catalyzes the chemical reaction
In enzymology, a riboflavin kinase is an enzyme that catalyzes the chemical reaction
The α-aminoadipate pathway is a biochemical pathway for the synthesis of the amino acid L-lysine. In the eukaryotes, this pathway is unique to several species of yeast, higher fungi, and the euglenids. It has also been reported from bacteria of the genus Thermus and also in Pyrococcus horikoshii, potentially suggesting a wider distribution than previously thought. This uniqueness of the pathway makes it a potentially interesting target for antimycotics.
Phosphoribosylglycinamide formyltransferase (EC 2.1.2.2, 2-amino-N-ribosylacetamide 5'-phosphate transformylase, GAR formyltransferase, GAR transformylase, glycinamide ribonucleotide transformylase, GAR TFase, 5,10-methenyltetrahydrofolate:2-amino-N-ribosylacetamide ribonucleotide transformylase) is an enzyme with systematic name 10-formyltetrahydrofolate:5'-phosphoribosylglycinamide N-formyltransferase. This enzyme catalyses the following chemical reaction
The enzyme 3,4-dihydroxy-2-butanone 4-phosphate synthase (RibB) EC 4.1.99.12 catalyses the conversion of D-ribulose 5-phosphate to formate and 3,4-dihydroxy-2-butanone 4-phosphate, the latter serving as the biosynthetic precursor for the xylene ring of riboflavin. In Photobacterium leiognathi, the riboflavin synthesis genes ribB, ribE, ribH and ribA all reside in the lux operon. RibB is sometimes found as a bifunctional enzyme with GTP cyclohydrolase II that catalyses the first committed step in the biosynthesis of riboflavin. No sequences with significant homology to DHBP synthase are found in the metazoa.
2-amino-3,7-dideoxy-D-threo-hept-6-ulosonate synthase is an enzyme with systematic name L-aspartate 4-semialdehyde:1-deoxy-D-threo-hexo-2,5-diulose 6-phosphate methylglyoxaltransferase. This enzyme catalyses the following chemical reaction
Isopentenyl phosphate kinase is an enzyme with systematic name ATP:isopentenyl phosphate phosphotransferase. This enzyme catalyses the following chemical reaction
2-amino-5-formylamino-6-ribosylaminopyrimidin-4(3H)-one 5'-monophosphate deformylase (EC 3.5.1.102, ArfB) is an enzyme with systematic name 2-amino-5-formylamino-6-(5-phospho-D-ribosylamino)pyrimidin-4(3H)-one amidohydrolase. This enzyme catalyses the following chemical reaction
2,5-diamino-6-hydroxy-4-(5-phosphoribosylamino)pyrimidine is a metabolite in the purine metabolism, formed by the hydrolysis of GTP by GTP cyclohydrolase II. Alternatively two separate enzymes can carry out this reaction, initially GTP cyclohydrolase IIa hydrolyses the 8,9 bond to form 2-Amino-5-formylamino-6-(5-phospho-D-ribosylamino)pyrimidin-4(3H)-one, followed by de-formylation by 2-amino-5-formylamino-6-ribosylaminopyrimidin-4(3H)-one 5'-monophosphate deformylase. 2,5-diamino-6-hydroxy-4-(5-phosphoribosylamino)pyrimidine is deaminated by Diaminohydroxyphosphoribosylaminopyrimidine deaminase to form 5-amino-6-(5-phosphoribosylamino)uracil.
