Bacterial decarboxylases

Amine build-up in fish muscle usually results from decarboxylation of amino acids in the muscle by enzymes of bacterial origin. This review will present information on the activity of bacterial decarboxylases and the formation of amines in fish. Mechanisms of decarboxylase action and production of bacterial decarboxylases in fish muscle are discussed. Emphasis is placed upon studies dealing with formation of histidine decarboxylase and histamine. Histamine, because of its involvement in Scombroid food poisoning, has been extensively studied with regard to its formation in fish and fishery products. 

Because amine formation in fish muscle and other foods usually results from bacterial growth with concomitant production of a bacterial decarboxylase, this paper will concentrate on the mechanisms of bacterial decarboxylation and factors influencing the production and activity of the enzymes. Also, because of the overall scope of the subject, the availability of excellent reviews on bacterial decarboxylation (2, 3) and the public health importance of histamine in fish and fishery products, this paper will primarily be limited to a discussion of histidine decarboxylase (EC 4.1.1.22) and the formation of histamine in fish muscle. 

Table I. Historical Perspective on Bacterial Decarboxylases Amino Acid...

Factors that Influence Bacterial Decarboxylase Production... 

Although the sequence similarity of both bacterial decarboxylases is low (<30%) their three-dimensional (3D) structures are highly similar, showing compact ho-motetramers [2,3]. The main difference between the two structures is the length of the C-terminal helix, which is 40 amino acids longer in PDC (568 aa per subunit) than BFD (528 aa per subunit). 

The 631 nucleotide region, on analysis, showed restriction sites for a large number of restriction enzymes like Kpnl, SauSA, Smal, Xbal, Xmal, Sail (one site each), etc. The sequence had higher GC content, with 28.0% C and 29.3% G residues, than AT content the percentages of A and "F were 23.3 and 19.4, respectively. It codes for a polypeptide of about 21 kD. However, the nature of the protein and the mechanism of degradation of BOAA is not understood. Homology search did not reveal any homology with any of the known bacterial decarboxylase or deaminase which are present in our data base. 

Gale studied the formation of bacterial decarboxylases for arginine, lysine, ornithine, histidine, tyrosine, and glutamic acid. One result of his studies was the demonstration that these enzymes occur in variable amounts in the cells and that environmental conditions, such as pH of the medium, influence the amount of enzyme formed. The failure to... 

Below pH 5-5 carbon dioxide is released and the net effect is the loss of the carboxyl group and removal of a proton so that the pH of the medium tends to rise. The free amino acids which act as substrates for the reaction are derived from (1) the saliva and gingival fluid, (2) the hydrolysis of proteins present in the plaque matrix, and (3) bacterial syntheses. The bacterial decarboxylases have pH optima on the acid side of neutrality (pH 4-5 >0). They are inducible enzymes and are synthesized only when amino acids are present and the pH is low. This... 

Kikuchi Y, H Kojima, T Tanaka, Y Takatsuka, Y Kamio (1997) Characterization of a second lysine decarboxylase isolated from Escherichia coli. J Bacterial 179 4486-4492. 

Poelarends GJ, WH Johnson, AG Murzin, CP Whitman (2003) Mechanistic characterization of a bacterial malonate semialdehyde decarboxylase. J Biol Chem 278 48674-48683. 

A group of enzymes which may be employed in the measurement of L amino acids are the L-amino acid decarboxylases (EC 4.1.1) of bacterial origin, many of which are substrate specific. They catalyse reactions of the type ... 

Gale, E. (1946). The bacterial amino acid decarboxylases, Adv. Enzymol. Relat. Subjects... 

For reactions in which one or more reactants or products is a gas, manometry (the measurement of pressure differences) can provide a convenient means for monitoring the course and kinetics of the reaction Thus, enzymes that can be assayed with this method include oxidases, urease, carbonic anhydrase, hydrogenase, and decarboxylases. For example, bacterial glutamate decarboxylase is readily assayed by utilizing a Warburg flask and measuring the volume of gas evolved at different times using a constant-pressure respirometer. ... 

The principal pathways for the biogenesis and metabolism of histamine are well known. Histamine is formed by decarboxylation of the amino acid, L-histidine, a reaction catalyzed by the enzyme, histidine decarboxylase. This decarboxylase is found in both mammalian and non-mammalian species. The mammalian enzyme requires pyridoxal phosphate as a cofactor. The bacterial enzyme has a different pH optimum and utilizes pyruvate as a cofactor (26.27). 

Relationship of Bacterial Histidine Decarboxylase Production to Histamine Formation. Many studies have been completed with the objective of understanding factors such as storage time and temperature that influence production of histamine in fish. The majority of the investigations have considered only the histamine content of the product, and, consequently, only limited information is available concerning the relationship of histidine decarboxylase formation by the microflora to histamine build-up. 

Many of the proteins of membranes are enzymes. For example, the entire electron transport system of mitochondria (Chapter 18) is embedded in membranes and a number of highly lipid-soluble enzymes have been isolated. Examples are phosphatidylseiine decarboxylase, which converts phosphatidylserine to phosphatidylethanolamine in biosynthesis of the latter, and isoprenoid alcohol phosphokinase, which participates in bacterial cell wall synthesis (Chapter 20). A number of ectoenzymes are present predominantly on the outsides of cell membranes.329 Enzymes such as phospholipases (Chapter 12), which are present on membrane surfaces, often are relatively inactive when removed from the lipid environment but are active in the presence of phospholipid bilay-ers.330 33 The distribution of lipid chain lengths as well as the cholesterol content of the membrane can affect enzymatic activities.332... 

By 1998, X-ray structures had been determined for four thiamin diphosphate-dependent enzymes (1) a bacterial pyruvate oxidase,119120 (2) yeast and bacterial pyruvate decarboxylases,121 122c (3) transketolase,110123124 and (4) benzoylformate decarboxylase.1243 Tire reactions catalyzed by these enzymes are all quite different, as are the sequences of the proteins. However, the thiamin diphosphate is bound in a similar way in all of them. 

Most known thiamin diphosphate-dependent reactions (Table 14-2) can be derived from the five halfreactions, a through e, shown in Fig. 14-3. Each halfreaction is an a cleavage which leads to a thiamin- bound enamine (center, Fig. 14-3) The decarboxylation of an a-oxo acid to an aldehyde is represented by step b followed by a in reverse. The most studied enzyme catalyzing a reaction of this type is yeast pyruvate decarboxylase, an enzyme essential to alcoholic fermentation (Fig. 10-3). There are two 250-kDa isoenzyme forms, one an a4 tetramer and one with an ( P)2 quaternary structure. The isolation of ohydroxyethylthiamin diphosphate from reaction mixtures of this enzyme with pyruvate52 provided important verification of the mechanisms of Eqs. 14-14,14-15. Other decarboxylases produce aldehydes in specialized metabolic pathways indolepyruvate decarboxylase126 in the biosynthesis of the plant hormone indoIe-3-acetate and ben-zoylformate decarboxylase in the mandelate pathway of bacterial metabolism (Chapter 25).1243/127... 

Histidine (bacterial) S-Adenosylmethionine Aspartate a- decarboxylase (3-Alanine... 

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