Substrate specificity, decarboxylase

By contrast, the cytoplasmic decarboxylation of dopa to dopamine by the enzyme dopa decarboxylase is about 100 times more rapid (Am 4x 10 " M) than its synthesis and indeed it is difficult to detect endogenous dopa in the CNS. This enzyme, which requires pyridoxal phosphate (vitamin B6) as co-factor, can decarboxylate other amino acids (e.g. tryptophan and tyrosine) and in view of its low substrate specificity is known as a general L-aromatic amino-acid decarboxylase. 

The occurrence of 3,4-dihydroxybenzoate decarboxylase was also found widely in facultative anaerobes. Among them, Enterobacter cloacae P241 showed the highest activity of 3,4-hydroxybenzoate decarboxylase, and the activity of the cell-free extract of E. cloacae P241 was determined to be 0.629 p.mol min (mg protein) at 30°C, which was more than that of C. hydroxybenzoicum, 0.11 (xmol min mg protein)" at 25°C. The E. cloacae P241 enzyme has a molecular mass of 334 kDa and consists of six identical 50 kDa subunits. The value for 3,4-dihydroxybenzoate was 177 p.M. The enzyme is also characteristic of its narrow substrate specificity and does not act on 4-hydroxybenzoate and other benzoate derivatives. The properties of E. cloacae P241 3,4-hydroxybenzoate decarboxylase were similar to those of C. hydroxybenzoicum in optimum temperature and pH, oxygen sensitivity, and substrate specificity. 

Although the absolute configurations of the products are opposite to that of antiinflammatory active compounds, and the substrate specificity is rather restricted as to the steric bulkiness around the reaction center, the enzyme system of A. bronchisepticus was proved to have a unique reactivity. Thus, detailed studies on the isolated enzyme were expected to elucidate some new interesting mechanism of the new type of decarboxylation. Thus, the enzyme was purified. (The enzyme is now registered as EC 4.1.1.76.) The molecular mass was about 24kDa. The enzyme was named as arylmalonate decarboxylase (AMDase), as the rate of the decarboxylation of phenylmalonic acid was faster than that of the a-methyl derivative. ... 

Drosophila DDC belongs to a family of pyridoxal-dependent decarboxylases that extends from prokaryotes to eukaryotic plants and animals. The members of this family show significant sequence similarity over much of their length, even though the individual proteins have quite different substrate specificities, including the amino acids tyrosine, tryptophan, phenylalanine, histidine, and glutamate, and the amino acid derivatives... 

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 ... 

In order to increase the understanding of ThDP-dependent enzymes, the identification of amino acid side chains important for the catalysis of the carboligase reaction in pyruvate decarboxylase from Zymomonas mohilis (E.C. 4.1.1.1) and benzoylformate decarboxylase from Pseudomonasputida (E.C. 4.1.1.7) was a major task. Using site-directed mutagenesis and directed evolution, various enzyme variants were obtained, differing in substrate specificity and enantioselectivity. 

M. Pohl, Exchanging the substrate specificities of pyruvate decarboxylase from Zymomonas mohilis and benzoylformate decarboxylase from Pseudomonas putida. Protein Eng. Des. 

B. Lingen, D. Kolter-Jung, P. Dtinkelmann, R. Feldmann, J. Grotzinger, M. Pohl, M. Muller, Alteration of the substrate specificity of benzoylformate decarboxylase from Pseudomonas putida by directed evolution. ChemBioChem 2003, 4, 721-726. 

Figure 16-6 shows schematically how the pyruvate dehydrogenase complex carries out the five consecutive reactions in the decarboxylation and dehydrogenation of pyruvate. Step CD is essentially identical to the reaction catalyzed by pyruvate decarboxylase (see Fig. 14-13c) C-l of pyruvate is released as C02, and C-2, which in pyruvate has the oxidation state of an aldehyde, is attached to TPP as a hydroxyethyl group. This first step is the slowest and therefore limits the rate of the overall reaction. It is also the point at which the PDH complex exercises its substrate specificity. In step (2) the hydroxyethyl group is oxidized to the level of a car-...

Numerous other amino acid decarboxylases have been isolated and characterized, and much interest has been shown as a result of the irreversible nature of the reaction with the release of C02 as the thermodynamic driving force. Although these enzymes have narrow substrate-specificity profiles, their utility has been widely demonstrated. Additional industrial processes will continue to be developed once other decarboxylases become available. Such biocatalysts would include the aromatic amino acid (E.C. 4.1.1.28), phenylalanine (E.C. 4.1.1.53) and tyrosine (E.C. 4.1.1.25) decarboxylases, which likely could be used to produce derivatives of their respective substrates. These derivatives are finding increased use in the development of peptidomimetic drugs and as possible positron emission tomography imaging agents.267-268... 

All terpenoid indole alkaloids are derived from tryptophan and the iridoid terpene secologanin (Fig. 2b). Tryptophan decarboxylase, a pyridoxal-dependent enzyme, converts tryptophan to tryptamine (62, 63). The enzyme strictosidine synthase catalyzes a stereoselective Pictet-Spengler condensation between tryptamine and secologanin to yield strictosidine. Strictosidine synthase (64) has been cloned from the plants C. roseus (65), Rauwolfla serpentine (66), and, recently, Ophiorrhiza pumila (67). A crystal structure of strictosidine synthase from R. serpentina has been reported (68, 69), and the substrate specificity of the enzyme can be modulated (70). 

Guo, Z., Goswami, A., Nanduri, V. B., Patel, R. N. Asymmetric acyloin condensation catalysed by phenylpyruvate decarboxylase. Part 2 Substrate specificity and purification of the enzyme. Tetrahedron Asymmetry 200, 12, 571-577. 

A number of amines derived from aromatic amino acid are present in brain in trace quantities. Since aromatic L-amino acid decarboxylase shows a broad substrate specificity, it is not surprising that compounds such as tyramine, tryptamine, phenylethylamine, and histamine are present in brain. These amines are derived from the simple decarboxylation of the corresponding... 

Within each of these sublineages, the type of catalyzed reaction was mostly conserved, whereas the substrates varied. For example, all the enzymes in the ATII subfamily are aminotransferases, with the only apparent exception of dialkylglycine decarboxylase, which, however, catalyzes a decarboxylation-dependent transamination (the enzyme cannot directly transaminate its substrate, which lacks an ct-proton, but proceeds to decarboxylate it and then catalyzes a transamination with the decarboxylation product)." Hence, the evolutionary tree shows that, in general, specialization for reaction type came first, whereas the last and shortest phase of the evolutionary history involved specialization for substrate specificity. 

When the development of more sensitive techniques and the introduction of new inhibitors had made more detailed studies possible, it became clear that mammalian histidine decarboxylases could themselves be divided into two sub-classes, one having optimum activity in the range pH 6-7, and the other in the range pH 8-0-9-5 > . Other differences between these two enzymes then became apparent, the most notable being in their substrate specificity . Solutions of the enzyme having the lower pH optimum were found to act only on L-histidine. Solutions of the other enzyme were capable of decarboxylating a number of amino acids structurally related to histidine. These enzymes will be referred to as specific and non-specific histidine decarboxylase, respectively. 

The histidine decarboxylase which has its maximum activity in the pH range 6-0 7-0 appears to be substrate-specific, acting only on L-histidine. This enzyme, which will be referred to as specific histidine decarboxylase, has been detected in various tissues, notably in mast cells, in the glandular portion of rat stomach, in rat foetal liver, and in certain tumours. Histidine decarboxylase activity which has been shown to be induced in tissues of various species when the animals are subjected to stressful stimuli also has many of the properties of specific histidine decarboxylase. Some comparative properties of the two types of histidine decarboxylase derived from various mammalian sources are given in Table 4.4. 

The function of the non-specific histidine decarboxylase of rabbit- or guinea-pig liver and kidney remains to be clarified. However, in view of its wide substrate specificity [Table 4.3), this enzyme may rather be a general aromatic L-amino acid decarboxylase, the purpose of which is to produce other physiologically important amines in addition to histamine. 

Tryptophan is a product of the shikimate pathway and is converted into tryptamine by tryptophan decarboxylase (TDC), Fig. (4). TDC is a cytosolic soluble enzyme that occurs as a dimeric protein, and it was shown to exhibit a high substrate specificity and to be under post-translational control [46-52]. A cDNA clone encoding TDC was isolated by DeLuca et al. [53] and the full gene was characterized by Gooddijn et al. [54, 55] who found that TDC is encoded by a single copy gene without introns. The Tdc promoter has also been cloned and its regulation characterized [56, 57]. 

Some microorganisms associated with fruit and vegetable fermentations may cause the enzymatic formation of BA from free amino acids by the activity of substrate-specific amino acid decarboxylases. BA are small biologically active organic bases and are both physiologically/chemically and pharmacologically of great interest. They interfere in... 

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