Acetyl phosphate utilization

Biosynthesis and Utilization of Acetyl Phosphate, Formyl Phosphate, and Carbamyl Phosphate and their Relations to the Urea Cycle... 

Animal and bacterial enzymes that utilize or synthesize carbamyl phosphate have activity with acetyl phosphate. Acyl phosphatase hydrolyzes both substrates, and maybe involved in the specific dynamic action of proteins. Ornithine and aspartic transcarbamylases also synthesize acetylornithine and acetyl aspartate. Finally, bacterial carbamate kinase and animal carbamyl phosphate synthetase utilize acetyl phosphate as well as carbamyl phosphate in the synthesis of adenosine triphosphate. The synthesis of acetyl phosphate and of formyl phosphate by carbamyl phosphate synthetases is described. The mechanism of carbon dioxide activation by animal carbamyl phosphate synthetase is reviewed on the basis of the findings concerning acetate and formate activation. 

Mg 2 were required for the reaction to proceed. The acetyl phosphate is utilized for the synthesis of acetyl-CoA, required for lysine degradation. The importance of Stadtman s finding becomes apparent upon close examination of the experimental data. 

Lactobacillus, Leuconostoc and Bifidobacterium employ the PK pathway as the central fermentative pathway. PK catalyses the cleavage of a ketose phosphate (donor substrate such as o-xylulose 5-phosphate), utilizing an inorganic phosphate (acceptor substrate) to produce an aldose phosphate released from the donor (first product such as glyceraldehyde 3-phosphate), water (second product) and acetyl phosphate (third product) (Figure 4.3). The first half of the reaction of PK is identical to that of TK. However, the subsequent reaction catalysed by PK is distinct from TK (Yevenes and Frey 2008). PK releases a water molecule (dehydration) from the a,p-dihydroxyethyl ThDP intermediate to form the acetyl ThDP intermediate, and then a nucleophilic attack of the acceptor substrate (phosphate) on the acetyl ThDP intermediate yields the third product (acetyl phosphate). The crystal structures of the intermediates before and after the dehydration step have been reported (Suzuki et al. 2010). 

Phosphoketolase catalyses cleavage of sugar phosphates utilizing an inorganic phosphate to produce water, acetyl phosphate, and a shortened sugar phosphate. 

The utilization of pentose phosphate without conversion to hexose is effected by Lactobacillus pentosus. An enzyme isolated from this organism converts xylulose-5-phosphate in one step to acetyl phosphate and triose phosphate (IX).This enzyme has been named phosphopentoketolase. 

An alternative large-scale synthesis of ATP is one that was recently developed by G. M. Whitesides, M.I.T., which utilizes acetyl phosphate as the phosphate donor and immobilized enzymes (see Section 4.7) as a catalyst (30). The reaction occurs under mild conditions (approximately neutral pH, room temperature), the insoluble polymeric catalyst is easily removed (centrifugation) and need be present only in small amounts, relative to the substrate and the reaction is more specific than a nonenzymatic synthesis (i.e., adenosine tetraphosphate is not formed as a by-product). The net reaction is ... 

In comparison to the homofermentative processes, within the heterofermentative route, glucose is not converted by the glycolysis pathway but by the pentose phosphate pathway. Fructose-1,6-bisphosphate-aldolase and triosephosphate isom-erase are not involved. The microorganisms are adapted to the utilization of pentoses as carbon source and in addition convert hexoses like glucose via this route. These pentoses are found when degrading plant material and are mainly xylose, ribose, or arabinose. They are converted via xylulose-5-phosphate which is converted to acetyl-phosphate and glycerinaldehyde-3-phosphate. Afterward,... 

The UDP-Gal epimerase system was also one of the early methods to employ pyruvate kinase (PK EC 2.7.1.40) for the conversion of UDP to UTP, with the simultaneous formation of pyruvate from phospho(enol)pyruvate (PEP). Previous kinase systems employed were either more expensive (nucleoside diphosphate kin-ase(EC 2.7.4.6)/ATP) or were thermodynamically less favorable (acetate kinase(EC 2.7.2.1)/acetyl phosphate). Another potentially usefid kinase system has recently been described. Noguchi and Shiba have utilized polyphosphate kinase (PPK) for the formation of UTP from UDP in a UDP-Gal recycling system [13]. Previously, PPK was shown to catalyze the reversible transfer of phosphate from ATP to ADP. Recently, it has been discovered that PPK will also accept other NDP and NTP substrates. For application to recycling systems, poly(phosphate) is more affordable than PEP as a phosphoryl donor. Synthetically, replacement of PK with PPK in the UDPGE-based recycling system efficiently provided LacNAc from GlcNAc on a multi-gram scale. 

Synthetic studies for sialic acid and its modifications have extensively used the catabolic enzyme N-acetylneuraminic acid aldolase (NeuA E.C. 4.1.3.3), which catalyzes the reversible addition of pyruvate (70) to N-acetyl-D-mannosamine (ManNAc, 11) to form the parent sialic acid N-acetylneuraminic acid (NeuSNAc, 12 Scheme 2.2.5.23) [1, 2, 45]. In contrast, the N-acetylneuraminic acid synthase (NeuS E.C. 4.1.3.19) has practically been ignored, although it holds considerable synthetic potential in that the enzyme utilizes phosphoenolpyruvate (PEP, 71) as a preformed enol nucleophile from which release of inorganic phosphate during... 

Ketols can also be formed enzymatically by cleavage of an aldehyde (step a, Fig. 14-3) followed by condensation with a second aldehyde (step c, in reverse). An enzyme utilizing these steps is transketolase (Eq. 17-15),132b which is essential in the pentose phosphate pathways of metabolism and in photosynthesis. a-Diketones can be cleaved (step d) to a carboxylic acid plus active aldehyde, which can react either via a or c in reverse. These and other combinations of steps are often observed as side reactions of such enzymes as pyruvate decarboxylase. A related thiamin-dependent reaction is that of pyruvate and acetyl-CoA to give the a-diketone, diacetyl, CH3COCOCH3.133 The reaction can be viewed as a displacement of the CoA anion from acetyl-CoA by attack of thiamin-bound active acetaldehyde derived from pyruvate (reverse of step d, Fig. 14-3 with release of CoA). 

After developing procedures for the activation and coupling of anomeric trichloroacetimidate and glycosyl phosphate donors as well as for the deprotection of acetyl and levulinoyl esters, we designed a synthesis utilizing all aspects of our automated chemistry. Trisaccharide 24, composed of three... 

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