Purification and Properties of an α-Dialkyl Amino Acid Transaminase<sup>*</sup>

Bailey, Gordon B.; Dempsey, Walter B.

doi:10.1021/bi00857a039

Cited by 50 publications

(43 citation statements)

References 14 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…This specificity for C4′ protonation in the decarboxylation of AIB is enigmatic since the transamination half-reaction is fully reversible (2), demonstrating that the quinonoid intermediate produced from deprotonation of L-alanine can be reprotonated on either C R or the coenzyme C4′. Herein, models are proposed to account for this difference in reaction specificity and are discussed in the light of the data presented.…”

mentioning

confidence: 96%

See 1 more Smart Citation

Reactions of Alternate Substrates Demonstrate Stereoelectronic Control of Reactivity in Dialkylglycine Decarboxylase

1998

View full text Add to dashboard Cite

Kinetic and product analyses of the reactions of dialkylglycine decarboxylase with several alternative substrates are presented. Rate constants for the reactions of amino and keto acids of several substrates decrease logarithmically with increasing side-chain size. Conversely, k cat for L-amino acid decarboxylation increases with side-chain size. These and other data confirm a proposed model for three binding subsites in the active site. In this model, bond making and breaking in both the decarboxylation and transamination half-reactions occurs at the "A" subsite, which maintains the scissile bond aligned with the p orbitals of the conjugated aldimine and thus maximizes stereoelectronic effects. This strongly supports the proposal by Dunathan (Proc. Natl. Acad. Sci. U.S.A. 55,[712][713][714][715][716]) that PLP-dependent enzymes can largely control reaction specificity by specific orientation about C R in the external aldimine intermediate. The "B" subsite can accept either an alkyl or a carboxylate group, while the "C" subsite accepts only small alkyl groups. This model predicts the existence of nonproductive binding modes for amino acids, which is proposed to be the ultimate origin of the k cat increase with side-chain size for L-amino acid decarboxylation. The specificity of the 2-aminoisobutyrate decarboxylation half-reaction toward oxidative decarboxylation is very high (<1 in 10 5 turnovers yields nonoxidative decarboxylation). The origin of this specificity is explored with the reactions of amino-and methylaminomalonate. These substrates exhibit high yields of nonoxidative decarboxylation, providing support for a model in which the interaction between a carboxylate group in the B subsite and Arg406 is a prerequisite to proton donation to and removal from C R .Dialkylglycine decarboxylase (DGD) 1,2 from Pseudomonas cepacia is a PLP dependent enzyme that catalyzes the oxidative decarboxylation of 2,2-dialkylglycines, yielding CO 2 , a ketone, and the PMP form of the enzyme (Scheme 1). The catalytic cycle is completed by transamination of an R-keto acid, preferentially pyruvate (1-3). The overall reaction catalyzed by DGD is shown below. The unusual ability of DGD to catalyze rapidly two classical PLPdependent reactions has rekindled an interest in this enzyme.The X-ray structure of DGD has been determined to 2.1-Å resolution (4, 5). The fold of the enzyme is roughly similar to the well-studied aspartate aminotransferase (6), which is a member of evolutionary subgroup I of aminotransferases (7). DGD is a representative member of evolutionary subgroup II (8), and its fold is closely similar to the other known structures of subgroup II enzymes (9, 10). The active site structure of DGD is similar to that of aspartate aminotransferase in that the interactions made between coenzyme and protein are highly conserved (5).Toney et al. (5) proposed a structurally based model of the active site of DGD in which there are three binding subsites (A-C) that differ in their functional group specificities. One of t...

show abstract

mentioning

confidence: 96%

“…The catalytic cycle is completed by transamination of an R-keto acid, preferentially pyruvate (1)(2)(3). The overall reaction catalyzed by DGD is shown below.…”

mentioning

confidence: 99%

Reactions of Alternate Substrates Demonstrate Stereoelectronic Control of Reactivity in Dialkylglycine Decarboxylase

1998

View full text Add to dashboard Cite

show abstract

“…Similar results were obtained in the experiments for L-alanine: aketo butyrate aminotransferase activity of AlB decomposing enzyme. a-Ketobutyrate pro- Pyruvate concentration: (1) 50 mM, (2) 10 mM, (3) 1 mM. Enzyme: 0.073 u. duced substrate inhibition, and at the lower concentrations reciprocal plots of velocities against the concentrations of L-alanine at three different concentrations of a-ketobutyrate give parallel lines (Fig.…”

Section: Effect Of Substrate Concentration On Alb Decomposing Enzyme mentioning

confidence: 89%

Kinetic Studies onα-Aminoisobutyrate Decomposing Enzyme

Honma

Shimomura

1974

Agricultural and Biological Chemistry

View full text Add to dashboard Cite

“…Therefore, the substrates containing hydroxymethyl group were more strongly decarboxylated by the fungus enzyme, being compared with the bacterial enzyme. o (0) 60 (8) 7 (10) 123 (96) 100 (100) 10 ~13) 4 (1) o (0)…”

mentioning

confidence: 99%