Phosphoenolpyruvate‐dependent flavinylation of 6‐hydroxy‐D‐nicotine oxidase

Abstract

The reaction leading to the flavinylation of apo-6-hydroxy-~-nicotine oxidase was investigated in cell-free extracts of Eschericia coli carrying the 6-hydroxy-~-nicotine oxidase (6-HDNO) gene on the expression plasmid pDB222. It was demonstrated that the reaction required phosphoenolpyruvate (P-pyruvate) in addition to FAD. When [32P]P-pyruvate or [14C]P-pyruvate were used in the reaction with apo-6-HDN0, no phosphorylated or pyruvylated apo-protein could be detected, however. In order to drive the reaction to completion, FAD and Ppyruvate had to be present simultaneously in the reaction mixture. When apo-6-HDN0, highly purified by affinity chromatography, was used in the reaction with P-pyruvate and FAD, no additional protein fraction was required. A possible reaction scheme for the formation of holoenzyme from 6-HDNO is discussed.Enzymes which are covalently modified by the attachment of their cofactor to the side chain of a specific amino acid residue represent a special category of post-translational modifications. The functional significance of these modifications and how they are accomplished is poorly understood. The covalent attachment of biotin to a specific lysine residue of carboxylases [l] and of heme to two specific cysteine residues of cytochrome c [2] are known to take place enzymatically. No corresponding holoenzyme synthetase, however, has been described so far for enzymes carrying covalently bound lipoic acid or covalently bound flavin. Both flavin cofactors, FAD as well as FMN, have been described as occurring in covalent linkage [3]. Biotin and lipoic-aciddependent enzymes always contain the cofactor bound to the polypeptide chain by a specific lysine residue [4]. Among the cytochromes, only cytochromes c andfcarry heme [5], always covalently bound by two essential cysteine residues. The situation with FAD, the primary flavin cofactor, is different. This cofactor is tightly but noncovalently bound in the majority of enzymes. In different covalently flavinylated enzymes, FAD is bound to the side chain of different amino acid residues. The 8a-methyl group of the FAD isoaloxazine ring is linked to the N1 or N3 of a histidine, to the sulfur of a cysteine or the oxygen of a tyrosine residue; 6-S-cysteinyl-FMN was also identified in some enzymes (reviewed in [3]). In addition to the differences in type of FAD linkage to the protein moiety, no amino acid sequence similarities surrounding the amino acid residue involved in FAD binding have been found thus far between covalently flavinylated enzymes. This situation is in contrast to information obtained from other examples of covalent modification of enzymes by cofactors where similar binding sequences are present [2, 3, 61. The question of whether the same mechanism accounts for €he covalent attachCorrespondence to R. Brandsch, Biochemisches Institut, Universit i t Freiburg, Hermann-Herder-StraBe 7, D-7800 Freiburg, Federal Republic of Germany Abbreviations. 6-HDNO, 6-hydroxy-~-nicotine oxidase; P-pyruvate, phosphoenolpyruvate.Enzyme. 6-Hydroxy-~-ni...

On the importance of the support material for enzymatic synthesis in organic media

“…The CPG beads were in the size range 200-400 mesh and had a mean pore diameter of 214.7 nm and a specific surface area of 7.4 m2/g. Hexyl-CPG and glucose-CPG were prepared as previously described [6]. Celite (30 -80 mesh) was obtained from BDH; it was washed thoroughly with ethanol and water and dried at 105 "C before use.…”

“…When enzymes are deposited on support materials in order to make them practical to use in organic media, the properties of the support influence the catalytic activity of the enzyme to a large extent [6]. One important parameter in this context is the capacity of the support to adsorb water.…”

“…In mixtures containing enzymes deposited on support materials in organic media water partitions between the enzyme, the support and the solvent. It has been shown that the capacity of the supports to adsorb water (their aquaphilicity) plays an important role in their suitability as enzyme supports in organic media [6]. When enzymes were deposited on supports with low aquaphilicity, they expressed much higher catalytic activity than when supports with higher aquaphilicity were used.…”

Assembly of Lipoic Acid on Its Cognate Enzymes: an Extraordinary and Essential Biosynthetic Pathway

“…Indeed, the alignment of LIPT1 and Lip3 show two highly conserved clusters within the large domain that contain serine residues. It should be noted that serine proteases can act as amidotransferases when water is limiting (161)(162)(163).…”

Biocatalysis in non-conventional media: Medium engineering aspects (Technical Report)

“…Such good operational stability of chymotrypsin has also been observed in acetonitrile/water mixtures with moderate amounts of water. After 168 hours of reaction in media containing 2-4% v/v of water the residual activity is about 90% of the initial activity (Reslow et al, 1988b). The operational stability of mandelonitrile lyase in diisopropyl ether is poor if the substrate solution in solvent has not been presaturated with water (Wehtje et al, 1990).…”