P-hydroxybutyrate

Poly-P-hydroxybutyrate (PHB) is a biodegradable thermoplastic that is produced by several microorganism. The PHB synthesis has been characterized eutrophus and the operon iavolved ia PHB productioa has beea cloaed. Recombiaant E. coli straias that can produce high levels of... 

Ascorbic acid is involved in carnitine biosynthesis. Carnitine (y-amino-P-hydroxybutyric acid, trimethylbetaine) (30) is a component of heart muscle, skeletal tissue, Uver and other tissues. It is involved in the transport of fatty acids into mitochondria, where they are oxidized to provide energy for the ceU and animal. It is synthesized in animals from lysine and methionine by two hydroxylases, both containing ferrous iron and L-ascorbic acid. Ascorbic acid donates electrons to the enzymes involved in the metabohsm of L-tyrosine, cholesterol, and histamine (128). 

The steps in the subsequent utilization of muscle LCFAs may be summarized as follows. The free fatty acids, liberated from triglycerides by a neutral triglyceride lipase, are activated to form acyl CoAs by the mediation of LCFAcyl-CoA synthetase which is situated on the outer mitochondrial membrane. The next step involves carnitine palmitoyl transferase I (CPT I, see Figure 9) which is also located on the outer mitochondrial membrane and catalyzes the transfer of LCFAcyl residues from CoA to carnitine (y-trimethyl-amino-P-hydroxybutyrate). LCFAcyl... 

Under metabolic conditions associated with a high rate of fatty acid oxidation, the liver produces considerable quantities of acetoacetate and d(—)-3-liydroxyl)utyrate (P-hydroxybutyrate). Acetoacetate continually undergoes spontaneous decarboxylation to yield acetone. These three substances are collectively known as the ketone bodies (also called acetone bodies or [incorrectly ] ketones ) (Figure 22-5). Acetoacetate and 3-hydroxybu-... 

Incorporation of C02 into poly-p-hydroxybutyrate by a strain of Xanthomonas sp. that metabolizes propene or its oxide (Small and Ensign 1995 Allen and Ensign 1996)... 

Three compounds acetoacetate, P-hydroxybutyrate, and acetone, are known as ketone bodies. They are suboxidized metabolic intermediates, chiefly those of fatty acids and of the carbon skeletons of the so-called ketogenic amino acids (leucine, isoleucine, lysine, phenylalanine, tyrosine, and tryptophan). The ketone body production, or ketogenesis, is effected in the hepatic mitochondria (in other tissues, ketogenesis is inoperative). Two pathways are possible for ketogenesis. The more active of the two is the hydroxymethyl glutarate cycle which is named after the key intermediate involved in this cycle. The other one is the deacylase cycle. In activity, this cycle is inferior to the former one. Acetyl-CoA is the starting compound for the biosynthesis of ketone bodies. 

The other ketone bodies are derived from acetoacetate P-hydroxybutyrate, by reduction with the involvement of NAD-dependent hydroxybutyrate dehydrogenase, and acetone, by decarboxylation of acetoacetate with the participation of aceto-acetate decarboxylase ... 

The enzymes responsible for their metabolism, d-P-hydroxybutyrate dehydrogenase, acetoacetate-succinyl-CoA transferase and acetoacetyl-CoA-thiolase, are present in... 

I.H. Lee, J.Y. Park, D.H. Kho, M.S. Kim and J.K. Lee (2002) Reductive effect of H2 uptake and poly-P-hydroxybutyrate formate on nitrogenase-mediated H2 accumulation of Rhodobacter sphaeroides according to light intensity. Appl. Microbiol. Biotechnol. 

PolyCy-benzyl L-glutamate) (PBLG), 15 109 Poly(y-ketosulfide)s, optically active, 23 711 Poly(P-alanine), 1 292 Poly-P-hydroxybutyrate (PHB), 12 482 Polybetaines, 20 479-482 applications of, 20 482 preparation of, 20 480-481 solution properties of, 20 481-482 synthesis of, 20 479-481 Polyborates, 4 256-258 Polyborosiloxanes, in silicon carbide manufacture and processing, 22 533 Polybrominated diphenyl ethers (PBDEs), 13 142-143 20 56... 

With these improved techniques P-hydroxybutyrate, which penetrates mitochondria easily and is oxidized to acetoacetate using NAD+ as H acceptor, gave a P/O ratio of 3, the value equivalent to that from the reoxidation of NADH found by Lehninger. Succinate, which bypassed the NAD+/NADH step, gave a ratio of 2. When cytochrome c-Fe2+ was... 

Alcoholics can also develop ketoaddosis. In alcoholic ketoacidosis, 3-hydroxybutyrate is the major ketone body produced because there is usually a high NADH/NAD ratio in the hver. The urinary nitroprusside test detects only acetoacetate and may dramatically underestimate the extent of ketosis in an alcoholic. 3-Hydroxybutyrate levels (P-hydroxybutyrate) should always be measured in these patients. 

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