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aminopropanol phosphate biosynthesis I

The biosynthesis of |FRAME:ADENOSYLCOBINAMIDE| from |FRAME:CPD-691| requires the attachment of an aminopropanol group to the propionate side chain of the corrin ring. Isotope studies with cultures of microorganisms that biosynthesize vitamin B12 have clearly shown that the amino group and carbon chain of this part of cobalamin are both derived from |FRAME: THR| |CITS: [13416277]|. Initial work suggested that |FRAME: 1-AMINO-PROPAN-2-OL| might be formed from L-threonine by sequential action of two separate enzymes, namely |FRAME: EC-| and |FRAME: EC-| |CITS: [4577583]| (see |FRAME: PWY-7378|). These two enzymes have been purified from |FRAME: TAX-83333| and were shown to catalyze the proposed reactions in vitro |CITS: [359547]|. At the time it was proposed that |FRAME: 1-AMINO-PROPAN-2-OL| is the substrate for the |FRAME: MONOMER-13228 CbiB| enzyme, originally proposed to convert |FRAME:CPD-691| to |FRAME:ADENOSYLCOBINAMIDE| |CITS: [9446573]|. Suprisingly, a few years later a |FRAME: TAX-90371| mutant blocked in |FRAME:1-AMINO-PROPAN-2-OL| biosynthesis was found to be not defective in either of these two enzymes. Furthermore, the researchers could demonstrate that blocking the two enzymes does not effect B12 biosynthesis in this organism |CITS: [1551838]|. The mutation responsible for the phenotype was eventually traced to |FRAME: EC-| (|FRAME:G-9854|). This enzyme does not accept |FRAME:THR| as a substrate, and is specific to |FRAME:L-THREONINE-O-3-PHOSPHATE|. The authors suggested that the product of this reaction, |FRAME:R-1-AMINOPROPAN-2-YL-PHOSPHATE|, is the actual substrate for the |FRAME: MONOMER-13228 CbiB| enzyme, originally proposed to convert |FRAME:CPD-691| to |FRAME:ADENOSYLCOBINAMIDE| |CITS: [9446573]|. The evidence for this proposed pathway was strengthened by the discovery of |FRAME: EC-| (|FRAME: G-10070|) in |FRAME: TAX-90371|. This enzyme generates |FRAME:L-THREONINE-O-3-PHOSPHATE| from |FRAME:THR| |CITS: [18308727]|. Growth studies showed that pduX mutants were impaired for the synthesis of |FRAME: ADENOSYLCOBALAMIN| de novo and from |FRAME: CPD-9083|, but not from |FRAME: COBINAMIDE| |CITS: [18308727]|. It should be noted that homologs of |FRAME: G-10070| were only found in some proteobacteria, actinobacteria, and firmicutes. It is still not clear whether a different enzyme catalyzes the phosphorylation of |FRAME: THR| in other cobalamin-producing bacteria, or whether other pathway variants exist for aminopropanol phosphate biosynthesis in those organisms.

from BIOCYC source record: META_PWY-5443
Type: pathway
Taxonomic scope
conserved biosystem

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