3- Hydroxybutyrate oligomer hydrolase

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

Kobayashi T, Saito T (2003) Catalytic triad of intracellular poly(3-hydroxybutyrate) depolymerase (PhaZl) in Ralstonia eutropha H16. J Biosci Bioeng 96 487-492 Kobayashi T, Shiraki M, Abe T, Sugiyama M, Saito T (2003) Purification and properties of an intracellular 3-hydroxybutyrate-oligomer hydrolase (PhaZ2) in Ralstonia eutropha H16 and its identification as a novel intracellular poly(3-hydroxybutyrate) depolymerase. J Bacteriol 185 3485-3490... 

Sudesh K, Abe H, Doi Y (2000) Synthesis, structure and properties of polyhydroxyalkanoates biological polyesters. Prog Polym Sd 25 1503-1555 Sugiyama A, Shiraki M, Kobayashi T, Morikawa G, Yamamoto M, Yamaoka M, Saito T (2002) Cloning and sequencing of an intracellular D(-)-3-hydroxybutyrate oligomer hydrolase from Acidovorax sp. strain SAl and purification of the enzyme. Curr Microbiol 45 123-127... 

Intracellular PHB Depolymerase of Cupriavidus necator. Note that C. necator was previously known as Ralstonia eutropha, Wautersia eutropha, Alcaligenes eutropha and Hydrogenomonas eutropha. iPHB depolymerases of PHAscl-accumulating bacteria were not described before the year 2000 but since then not less than seven putative iPHB depolymerases and two 3-hydroxybutyrate oligomer hydrolases have been postulated for C. 

Hydrolysis of end-labeled 3-hydroxybutyrate oligomers by purified A. faecalis T poly(3HB) depolymerase showed that the enzyme mainly cleaved the second and third ester linkage from the hydroxyl terminus [69]. However, since the enzyme also hydrolyzes cyclic oligomers, the A. faecalis depolymerase has endo-hydrolase activity in addition to exo-hydrolase activity [18, 70]. Results of... 

The intracellular biodegradation pathway of PHB is illustrated and combined with the biosynthetic pathway in Fig. 14.9 (Muller and Seebach, 1993 Senior and Dawes, 1971, 1973 Doi et al, 1992b Haywood et al, 1988). PHB is first depolymerized by PHB depolymerase to produce the 7 -3-hydroxybutyric acid (7 -3-HB) or 7 -3HB oligomers. The latter is further depolymerized by oligomer hydrolase to 7 -3HB monomer. 7 -3HB is dehydrogenated with NAD into acetoacetic acid which follows esterification with CoA-SH to produce acetoacetyl-CoA by the action of acetoacetyl-CoA synthase with the aid of ATP. The acetoacetyl-CoA is degraded into acetyl-CoA by /3-ketothiolase. This compound then enters the tricarboxylic acid (TCA) cycle to transform carbon dioxide and water under aerobic conditions. 

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... 

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