3-Hydroxybutyrate dimer

Hydroxybutyrate Dimer-Hydrolases and 3-Hydroxybutyrate Oligomer-Hydrolases... 

During aging of PHVB in sterile water at pH 7 and 60 °C, 2-butenoic acid (crotonic acid), 2-pentenoic acid, 3-hydroxybutyric acid, 3-hydroxyvaleric acid, 3-hydroxybutyrate dimer, 3-hydroxybutyrate-3-hydroxyvalerate dimer and 3-hydroxyvalerate dimer were formed [99]. The weight loss was, however, only 2% after 200 days at 60 °C. Monomers, oligomers and derivatives, produced by dehydration at the OH-terminus were identified after alkaline hydrolysis of PHB [110]. In accordance CZE showed that the accelerated hydrolysis of PHB leads to the formation of hydroxyacid oligomers and a series of peaks formed by a side reaction leading to a C=C bond at the noncarboxylic acid end [111]. Kinetics of the abiotic hydrolysis of PHB in acid and alkaline media were monitored by following the forma-... 

Fig. 3. (a) Biosynthesis of SCL PHA 1,3-ketothiolase 2, NADPH-dependent acetoacetyl-CoA reductase 3, SCL PHA polymerase 4, SCL PHA depolymerase 5, d(-)-3-hydroxybutyrate-dimer hydrolase, (b) Biosynthesis of P(HB-co-HV), 1, 3-ketothiolase 2a, NADPH-dependent acetoacetyl-CoA reductase 2b, NADH-dependent acetoacetyl-CoA reductase 3, SCL PHA polymerase 4, fatty acyl-CoA dehydrogenase 5, enoyl-CoA hydratase. 

Intracellular PHB Depolymerase of Rhodospirillum rubrum. R. rubrum possesses a putative intracellular PHB depolymerase system consisting of a soluble PHB depolymerase, a heat-stable inactivator and a 3-hydroxybutyrate dimer hydrolase. It consists of one polypeptide of around 35 kDa and has a pH optima of 9 and temperature optima of 55 °C. The purified enzyme was inactive with dPHB. It does not show lipase, protease or esterase activity with p-nitrophenyl fatty acid esters. It is highly substrate specific. ... 

Tanaka Y, Saito T, Fukui T, Tanio T, Tomita K (1981), Purification and properties of D(-)-3-hydroxybutyrate-dimer hydrolase Ifom Zoogloea-ramigera I-16-M , Eur J Biochem, 118, 177-182. 

PhaZ Poly(3-hydroxybutyrate) depolymerase PhaZc Hydroxybutyrate-dimer hydrolase... 

The first products of enzymatic hydrolysis of poly(3HB) by purified poly(3HB) depolymerases are a mixture of monomeric and/or oligomeric 3-hydroxybuty-rate esters. Some enzymes are able to hydrolyze oligomers and dimers to monomeric 3-hydroxybutyrate after prolonged time of hydrolysis in the presence of an excess of the appropriate depolymerase. These poly(3HB) depolymerases have high endogenous dimer-hydrolase activities (e.g., the poly(3HB) depolymerases of Comamonas strains, P. stutzeri, S. exfoliatus, and the depolymerases... 

Pterorhodine (113b)181 and drosopterin (133)182 are naturally occurring dimeric pteridines the former was synthesized from xanthopterin and acetone or acetaldehyde in the presence of ammonium sulfate or hydrogen peroxide,136 and the latter from 7,8-dihydropterin and j8-keto-a-hydroxybutyric acid.182b... 

In the former case, a bacterial or fungal colony on the surface of the material releases an extracellular degrading enzyme which breaks down the polymer chains into smaller units (dimers and ohgomers), which then are absorbed through the microorganisms ceU membrane and metabolised as a source of nutrient (carbon). It has been proposed that this mechanism first hydrolyses the chains of the amorphous phase of poly-(3-hydroxybutyrate) (PHB) and then proceeds to attack the chains in the crystalline state. The enzymatic degradation rate decreases as the crystallinity increases [15, 16]. 

The enzymatic hydrolysis of poly-p-hydroxybutyrate, PHB, by several different bacteria, which are known to secrete active esterases, has been studied in some detail by several research groups [7, 8]. As with the polysaccharides, the final products of these degradation reactions are the monomers, dimers and trimers, which are removed by hydrolysis only from hydroxyl-end of the polymer chain, as follows ... 

Figure 2.22a reports the DCI mass spectrum of a microbial copolyester, poly()3-hydroxybutyrate-co-15% )3-hydrox5rvalerate)(PFlB/HV). The relative intensities of several series of oligomers in the spectrum, from dimers to hexamers, are compared with theoretical intensities (Figure 2.22b). Each series...

As for poly(3-hydroxybutyrate), which is one of the representative bacterial polyesters, monomeric (butenoic) and oligomeric (mainly dimeric and trimeric) acids were reported to be observed in the pyrograms, which should be mostly formed through the six-membered transition state. Due to the presence of a methyl side chain, three types of isomeric structures can be produced for each oligomer, as shown in Figure 5.5. Among these, the trans type of inner olefinic products was usually dominant. 

Propylene is, next to ethylene, the most important basic chemical to produce not only polypropylene but also other intermediates for example propylene oxide and acrylonitrile. Just like ethylene, propylene can be produced via a hydrocarbon feedstock produced from a biomass [35-37]. Bio-glycerol produced as a byproduct of biodiesel can be dehydrogenated to produce propylene [48]. Bio-based ethylene can be dimerized to produce n-butene, which can then react with remaining ethylene via metathesis to produce propylene [49]. The use of fermentation products of biomass such as 1-butanol [50] enables the formation of n-butene, followed by a subsequent methathesis [49]. Alternatively, hydrothermal carboxylate reforming of fermentation products such as butyric acid or 3-hydroxybutyrate is also proposed as a viable option to propylene [51]. 

So far, biosynthesis of PHA can be summarized in eight pathways (Fig. 4, Table 1). The first pathway involves the three key enzymes (3-ketothiolase, NADPH-dependent acetoacetyl-CoA reductase, and PHA synthase encoded by genes phaA, phaB, and phaC, respectively. Ralstonia eutropha is the representative of this pathway. An associated pathway involving PHA degradation catalyzed by PHA depolymerase, dimer hydrolase, 3-hydroxybutyrate dehydrogenase, and acetoacetyl-CoA synthase helps regulate PHA synthesis and degradation. The associated pathway was found in strains of Aeromonas hydrophila. Pseudomonas stutzeri, R. eutropha, and Pseudomonas oleovorans (Sudesh et al. 2000). 

Tasaki O, Hiraide A, Shiozald T, Yamamura H, Ninomiya N, Sugimoto H (1999) The dimer and trimer of 3-hydroxybutyrate oligomer as a precursor of ketone bodies for nutritional care. J Parenter Enteral Nutr 23 321-325... 

Biodegradation in the environment involves extracellular enzymes secreted by microorganisms, and these enzymes have been collectively described as PHA depolymerases. Of the characterized depolymerases, most of them hydrolyze the PHA polymer into dimers, and the dimers are further hydrolyzed to the monomers by an extracellular or intracellular dimer hydrolase. The depolymerase from a Comamonas species, however, appears to hydrolyze poly(3HB) directly to 3-hydroxybutyrate (reviewed by Hocking and Marchessault 1994). Not surprisingly, the degree of crystallinity significantly affects the rate of PHA degradation, and it was concluded that poly(3HB) molecules in the amorphous state are more easily hydrolyzed than poly(3HB) in the crystalline state (reviewed by Steinbiichel 1996). 

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