Branched-chain keto acid decarboxylase

Fig. 10.23 Metabolism of L-isoleucine and of L-valine in man. Principal enzymes involved are 1, branched-chain keto acid decarboxylase 2, acyl-CoA hydratase 3, enoyl CoA hydratase 4, 3-hydroxyacyl-CoA dehydrogenase 5, 3-hydroxyisobutyryl-CoA hydrolase 6,2-methylacetoacetyl-CoA thiolase 7,3-hydroxyisobutyrate dehydrogenase.

The decarboxylation of branched chain keto acids is apparently carried out by the same decarboxylase (EC 4.1.1.1, Mg and thiamine pyrophosphate dependent) which is active on pyruvate in yeast (154, 167) and orange juice (168, 169). The latter enzyme acts on the keto acids derived from valine and isoleucine at about 15% of the pyruvate rate (169). Its activity declines rapidly (80% in 1 hour) in juice (pH 3.4). The malty flavor defect produced by S. lactis var. maltigenes, however, appears to be caused by a specific decarboxylase activity not found in other strains (158, 160) since simultaneous decarboxylation of pyruvate and a-ketoisocaproate was almost additive (163) while a-ketoisocaproate and a-ketoisovalerate competed with each other. Decarboxylation of... 

Rudiger, H.W., Langenbeck, U., Schulze-Schencking, M., Goedde, H.W. and Schuchmann, L. (1972), Defective decarboxylase in branched chain keto acid oxidase multienzyme complex in classical type of Maple Syrup Urine Disease. Hum. Genet., 14, 257. 

Mutation of the dihydrolipoate reductase component impairs decarboxylation of branched-chain a-keto acids, of pyruvate, and of a-ketoglutarate. In intermittent branched-chain ketonuria, the a-keto acid decarboxylase retains some activity, and symptoms occur later in life. The impaired enzyme in isovaleric acidemia is isovaleryl-CoA dehydrogenase (reaction 3, Figure 30-19). Vomiting, acidosis, and coma follow ingestion of excess protein. Accumulated... 

The broad synthetic potential ThDP-dependent enzymes for asymmetric C-C bond formation is by far not fully exploited with the acyloin- and benzoin-condensations discussed above. On the one hand, novel branched-chain a-keto-acid decarboxylases favorably extend the limited substrate tolerance of traditirnial enzymes, such as PDC, by accepting sterically hindered a-ketoacids as dcmors [1511], On the other hand, the acceptor range may be significantly widened by using carlxMiyl compounds other than aldehydes Thus, ketones, a-ketoacids and even CO2 lead to novel types of products (Scheme 2.203). 

Figure 14.2. Example of some metabolic pathways adopted by Lactobacillus plantarum during fermentation of vegetable and fruit juices. He, isoleucine Leu, leucine Val, valine His, histidine Glu, glutamic acid BcAT, branched-chain aminotransferase KDC, a-keto acid decarboxylase ADH, alcohol dehydrogenase MLE, malol-actlc enzyme HDC, histidine decarboxylase (Adapted from Filannino etal. 2014)...

Flavor-related activities of LAB depend on the species, with some specific activities found only in a small number of species. The branched-chain a-keto acid decarboxylase activity involved in the formation of malty branched-chain aldehydes from branched-chain AA, for example, has been found only in L lactis and not in the Lactobacillus and Leuconostoc strains tested (Fernandez De Palencia et al. 2006). Most LAB, however, display a great strain-to-strain variability, on the genomic level and/or at the phenotypic level. Table 19.3 gives some examples of intra- and interspecies variability of flavor-related LAB properties, such as proteolytic activities, AA-converting enzymatic activities, ester synthesis, and autolysis. 

A second variant form [90] is characterized by mental retardation (I.Q. 50) and no other evidence of neurological disease. The serum and urine levels of leucine, isoleucine, valine and the corresponding a-keto acids are in the leucinosis range continuously, not merely during infections. The leucocytes contained 15 to 25% of the normal activities of the branched chain a-keto acid decarboxylases. 

Thiamin-dependent enzymes, ACETOLACTATE SYNTHASE BENZOYLFORMATE DECARBOXYLASE BRANCHED-CHAIN a-KETO ACID DEHYDROGENASE COMPLEX... 

CWC Hu, KS Lau, TA Griffin, JL Chuang, CW Fisher, RP Cox, DT Chuang. Isolation and sequencing of a cDNA encoding the decarboxylase (El)-a precursor of bovine branched-chain a-keto acid dehydrogenase complex expression of El-a mRNA and subunit in maple-syrup-urine-disease and 3T3-L1 cells. J Biol Chem... 

Branched-chain Branched-chain a-keto-ketoaciduria or acid decarboxylase maple syrup urine (leukocytes) i (recessive)... 

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