Threonine phosphate

Okadaic acid Serine/threonine phosphate purposes seems not to be selective Leads to selective 18,64 ... 

Phosphorylated amino acids move in the order serine phosphate > threonine phosphate > tyrosine phosphate. 

RX— may be a thiol, a hydroxyl, or an indole group. In this way, serine, threonine, cysteine, tryptophan, cystathionine, and serine and threonine phosphates may be interconverted or degraded. 

Pyridoxal 5 -phosphate is an essential cofactor for many enzymes responsible for the metabolic conversions of amino acids. The fourth step in its synthetic pathway in Escherichia coli is catalyzed by the divalent metal ion-dependent enzyme 4-hydroxythreonine-4-phosphate dehydrogenase (PdxA), which converts 4-hydroxy-l-threonine phosphate (HTP) to 3-amino-2-oxopropyl phosphate. The... 

Abbreviations P , inorganic phosphate H-S-CoA, coenzyme A H4MPT, tetrahydromethanopterin [CO], enzyme-bound carbon monoxide H-S-CoM, coenzyme M H—S-HTP, A/-7-mercaptoheptanoyl-threonin phosphate. 

The (I( )-l-amino-2-propanol linker is known to be derived from threonine. In S. enterica, CobD was found to be an enzyme with L-threonine 0-3-phosphate decarboxylase activity, which generates (/f)-l-amino-2-propa-nol phosphate. The enzyme is a pyridoxal phosphate requiring enzyme and the structure of the protein has been determined by X-ray crystallography (Figure 28). The structure of CobD was found to be highly similar to the aspartate aminotransferase family of enzymes. Structures of CobD with substrate and product bound have allowed a detailed mechanism for the enzyme to be proposed, whereby the external aldimine is directed toward decarboxylation rather than aminotransfer. Threonine phosphate, itself, is synthesized from L-threonine by the action of a kinase, which is encoded by pduX The pduX is housed within the propanediol utilization operon rather than the cobalamin biosynthetic operon for reasons that are not clear. 

P. denitrificans CobD (cobinamide synthesis) and CobC (threonine phosphate decarboxylase). Together a and / were shown to catalyze the attachment of (if)-l-aminopropanol to adenosylcobyric acid in the presence of ATP (even if aminopropanol phosphate is likely to be the true substrate). 

Figure 28 The structure and mechanism of threonine phosphate decarboxyiase, CobD. (a) This enzyme of the anaerobic pathway identifies the active site by the presence of its pyridoxai phosphate cofactor (stick representation), which is attached to an active site iysine. (b) The mechanism of the enzyme invoives the binding of the threonine phosphate to the pyridoxai phosphate cofactor via a Schiff base. Foiiowing decarboxyiation, the product is released.

One aspect of archaeal corrinoid biosynthesis that remains to be verified is the formation of the l-amino-2-propanol linker in the lower ligand loop of the corrinoid. Possible sources include the reductive amination of lactaldehyde, the reductive amination of pyruvate, or the decarboxylation of threonine. Several bacteria have been shown to directly incorporate N-labeled threonine into aminopropanol and coenzyme Bi2- A threonine decarboxylase (CobD) has been detected in Streptomyces griseus and Salmonella typhimuriumP Studies with CobD from S. typhimurium LT2 were able to clearly demonstrate the decarboxylation of threonine-phosphate however, the timing of the decarboxylation could not be demonstrated and may occur prior to or after addition of the threonine-P to the corrin ring. " ... 

These results suggest that MJ0955 is a hisC and prohahly performs the annotated role in histidine biosynthesis. Thus, the identity of the threonine-phosphate decarboxylase remains to be determined. The possible involvement of a pyruvoyl-dependent enzyme in catalyzing this reaction should be considered. 

FIGURE 2 Phosphoamino add analysis of individual phospho-peptides (A-F) from p-labeled LC20. Pj, Ser-P, and Thr-P are labeled inorganic phosphate, serine-phosphate, and threonine-phosphate, respectively, and Pep-P is the unhydrolyzed P-labeled phosphate. From Erdddi et al. (1988a, Rg. 5, p. 587). 

Scheme 2.77 Resolutirai of roc-threonine ( -phosphate using acid phosphatase...

This activity was measured anaerobically by Gale and Stephenson as release of ammonia by bacterial cells. The system was not stable, but was protected by low concentrations of phosphate and reducing agents. At 0 C. inactivation occurred that was reversed by a boiled bacterial extract plus phosphate and a reducing agent. The reaction was better defined by Chargaff and Sprinson, who also studied the reaction in liver. Several bacterial species were found to deaminate both n- and L-serine and threonine. Phosphate-, methyl-, and ethyl-substituted hydroxyl groups prevented the reaction. 

Modifications such as phosphorylation are chemically simpler and are more easily identified by MS, although the addition of 80 Da can be due to either a phosphate (HPO3) or a sulfate (SO3). Serine and threonine phosphates are acid sensitive and may not survive LC/MS whereas tyrosine phosphates are generally more robust. Sulfate is also labile and may not be observed in positive ion MALDI but it usually can be identified by ESI or negative ion MALDI. The... 

Threonine phosphate gives rise to a doublet (Ho et ai, 1969), and no coupling has been observed or reported for other phosphoamino adds. It should finally be stated that the coupling between the phosphorus and the proton also allows for the study of the proton with the use of two-dimensional NMR techniques (Bolton, 1982 see Hutton, Chapter 16). 

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