|
Purinosome
The purinosome is a putative multi-enzyme complex that carries out de novo synthesis, ''de novo'' Purine metabolism#Biosynthesis, purine biosynthesis within the cell. It is postulated to include all six of the human enzymes identified as direct participants in this ten-step biosynthetic pathway converting phosphoribosyl pyrophosphate to inosine monophosphate: History Hypothesis The enzymes of the multi-step ''de novo'' Purine metabolism#Biosynthesis, purine biosynthesis pathway have been postulated to form a multi-enzyme complex to facilitate substrate channeling between each enzyme of the pathway. Slight variations of the pathway exists between phyla; however, there are 13 enzymes that can be considered part of this biosynthetic pathway. Several individual enzymatic functions have consolidated onto single bifunctional or trifunctional polypeptide chains in higher organisms, suggesting stable physical interactions exist between enzymes. The functional consolidation of steps ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Purine Metabolism
Purine metabolism refers to the metabolic pathways to synthesize and break down purines that are present in many organisms. Biosynthesis Purines are biologically synthesized as nucleotides and in particular as ribotides, i.e. bases attached to ribose 5-phosphate. Both adenine and guanine are derived from the nucleotide inosine monophosphate (IMP), which is the first compound in the pathway to have a completely formed purine ring system. IMP Inosine monophosphate is synthesized on a pre-existing ribose-phosphate through a complex pathway (as shown in the figure on the right). The source of the carbon and nitrogen atoms of the purine ring, 5 and 4 respectively, come from multiple sources. The amino acid glycine contributes all its carbon (2) and nitrogen (1) atoms, with additional nitrogen atoms from glutamine (2) and aspartic acid (1), and additional carbon atoms from formyl groups (2), which are transferred from the coenzyme tetrahydrofolate as 10-formyltetrahydrofolate, and ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
