On the mechanism of Escherichia coli pyridoxal kinase inhibition by pyridoxal and pyridoxal 5'-phosphate

Functional and structural properties of pyridoxal reductase (PdxI) from Escherichia coli: a pivotal enzyme in the vitamin B6 salvage pathway

Pyridoxine 4-dehydrogenase (PdxI), a NADPH-dependent pyridoxal reductase, is one of the key players in the Escherichia coli pyridoxal 5'-phosphate (PLP) salvage pathway. This enzyme, which catalyses the reduction of pyridoxal into pyridoxine, causes pyridoxal to be converted into PLP via the formation of pyridoxine and pyridoxine phosphate. The structural and functional properties of PdxI were hitherto unknown, preventing a rational explanation of how and why this longer, detoured pathway occurs, given that, in E. coli, two pyridoxal kinases (PdxK and PdxY) exist that could convert pyridoxal directly into PLP. Here, we report a detailed characterisation of E. coli PdxI that explains this behaviour. The enzyme efficiently catalyses the reversible transformation of pyridoxal into pyridoxine, although the reduction direction is thermodynamically strongly favoured, following a compulsory-order ternary-complex mechanism. In vitro, the enzyme is also able to catalyse PLP reduction and use NADH as an electron donor, although with lower efficiency. As with all members of the aldo-keto reductase (AKR) superfamily, the enzyme has a TIM barrel fold; however, it shows some specific features, the most important of which is the presence of an Arg residue that replaces the catalytic tetrad His residue that is present in all AKRs and appears to be involved in substrate specificity. The above results, in conjunction with kinetic and static measurements of vitamins B6 in cell extracts of E. coli wild-type and knockout strains, shed light on the role of PdxI and both kinases in determining the pathway followed by pyridoxal in its conversion to PLP, which has a precise regulatory function.

Cronobacter sakazakii Pyridoxal Kinase PdxY Mediated by TreR and pESA3 Is Essential for Vitamin B6 (PLP) Maintenance and Virulence

Cronobacter sakazakii is an opportunistic pathogen capable of causing severe infections, particularly in neonates. Despite the bacterium's strong pathogenicity, the pathogenicity of C. sakazakii is not yet well understood. Using a comparative proteomic profiling approach, we successfully identified pdxY, encoding a pyridoxal kinase involved in the recycling of pyridoxal 5'-phosphate (PLP), as a gene essential for the successful pathogenesis of C. sakazakii. Knocking out the pdxY gene resulted in slower growth and reduced virulence. Our study sheds light on the fundamental importance of pyridoxal kinase for the survival and virulence of C. sakazakii. The identification of pdxY as gene essential for successful pathogenesis provides a potential target for the development of new antibiotic treatments. IMPORTANCE The opportunistic pathogen Cronobacter sakazakii is known to cause severe infections, particularly in neonates, and can result in high mortality rates. In this study, we used a comparative proteomic profiling approach to identify genes essential for the successful pathogenesis of C. sakazakii. We successfully identified pdxY, encoding a pyridoxal kinase involved in the salvage pathway of pyridoxal 5'-phosphate (PLP), as a gene essential for the successful pathogenesis of C. sakazakii. Knocking out the pdxY gene resulted in impaired growth and reduced virulence. This study sheds light on the fundamental importance of pyridoxal kinase for the survival and virulence of C. sakazakii, which can be a potential target for the development of new antibiotic treatments. This study highlights the importance of comparative proteomic profiling in identifying virulence factors that can be targeted for the development of new antibiotics.

A direct enzymatic evaluation platform (DEEP) to fine-tuning pyridoxal 5'-phosphate-dependent proteins for cadaverine production

Pyridoxal 5'-phosphate (pyridoxal phosphate, PLP) is an essential cofactor for multiple enzymatic reactions in industry. However, cofactor engineering based on PLP regeneration and related to the performance of enzymes in chemical production has rarely been discussed. First, we found that MG1655 strain was sensitive to nitrogen source and relied on different amino acids, thus the biomass was significantly reduced when PLP excess in the medium. Then, the six KEIO collection strains were applied to find out the prominent gene in deoxyxylulose-5-phosphate (DXP) pathway, where pdxB was superior in controlling cell growth. Therefore, the clustered regularly interspaced short palindromic repeats interference (CRISPRi) targeted on pdxB in MG1655 was employed to establish a novel direct enzymatic evaluation platform (DEEP) as a high-throughput tool and obtained the optimal modules for incorporating of PLP to enhance the biomass and activity of PLP-dependent enzymes simultaneously. As a result, the biomass has increased by 55% using P_lacI promoter driven pyridoxine 5'-phosphate oxidase (PdxH) with a trace amount of precursor. When the strains incorporated DEEP and lysine decarboxylase (CadA), the cadaverine productivity was increased 32% due to the higher expression of CadA. DEEP is not only feasible for high-throughput screening of the best chassis for PLP engineering but also practical in fine-tuning the quantity and quality of enzymes.

Vitamin B-6-Induced Neuropathy: Exploring the Mechanisms of Pyridoxine Toxicity

Vitamin B-6 in the form of pyridoxine (PN) is commonly used by the general population. The use of PN-containing supplements has gained lots of attention over the past years as they have been related to the development of peripheral neuropathy. In light of this, the number of reported cases of adverse health effects due to the use of vitamin B-6 have increased. Despite a long history of study, the pathogenic mechanisms associated with PN toxicity remain elusive. Therefore, the present review is focused on investigating the mechanistic link between PN supplementation and sensory peripheral neuropathy. Excessive PN intake induces neuropathy through the preferential injury of sensory neurons. Recent reports on hereditary neuropathy due to pyridoxal kinase (PDXK) mutations may provide some insight into the mechanism, as genetic deficiencies in PDXK lead to the development of axonal sensory neuropathy. High circulating concentrations of PN may lead to a similar condition via the inhibition of PDXK. The mechanism behind PDXK-induced neuropathy is unknown; however, there is reason to believe that it may be related to γ-aminobutyric acid (GABA) neurotransmission. Compounds that inhibit PDXK lead to convulsions and reductions in GABA biosynthesis. The absence of central nervous system-related symptoms in PDXK deficiency could be due to differences in the regulation of PDXK, where PDXK activity is preserved in the brain but not in peripheral tissues. As PN is relatively impermeable to the blood-brain barrier, PDXK inhibition would similarly be confined to the peripheries and, as a result, GABA signaling may be perturbed within peripheral tissues, such as sensory neurons. Perturbed GABA signaling within sensory neurons may lead to excitotoxicity, neurodegeneration, and ultimately, the development of peripheral neuropathy. For several reasons, we conclude that PDXK inhibition and consequently disrupted GABA neurotransmission is the most plausible mechanism of toxicity.

Inhibiting Pyridoxal Kinase of Entamoeba histolytica Is Lethal for This Pathogen

Pyridoxal 5’-phosphate (PLP) functions as a cofactor for hundreds of different enzymes that are crucial to the survival of microorganisms. PLP-dependent enzymes have been extensively characterized and proposed as drug targets in Entamoeba histolytica. This pathogen is unable to synthesize vitamin B_6via de-novo pathway and relies on the uptake of vitamin B₆ vitamers from the host which are then phosphorylated by the enzyme pyridoxal kinase to produce PLP, the active form of vitamin B₆. Previous studies from our lab shows that EhPLK is essential for the survival and growth of this protozoan parasite and its active site differs significantly with respect to its human homologue making it a potential drug target. In-silico screening of EhPLK against small molecule libraries were performed and top five ranked molecules were shortlisted on the basis of docking scores. These compounds dock into the PLP binding site of the enzyme such that binding of these compounds hinders the binding of substrate. Of these five compounds, two compounds showed inhibitory activity with IC₅₀ values between 100-250 μM when tested in-vitro. The effect of these compounds proved to be extremely lethal for Entamoeba trophozoites in cultured cells as the growth was hampered by 91.5% and 89.5% when grown in the presence of these compounds over the period of 72 hours.

Knowns and Unknowns of Vitamin B6 Metabolism in Escherichia coli

Vitamin B₆ is an ensemble of six interconvertible vitamers: pyridoxine (PN), pyridoxamine (PM), pyridoxal (PL), and their 5'-phosphate derivatives, PNP, PMP, and PLP. Pyridoxal 5'-phosphate is a coenzyme in a variety of enzyme reactions concerning transformations of amino and amino acid compounds. This review summarizes all known and putative PLP-binding proteins found in the Escherichia coli MG1655 proteome. PLP can have toxic effects since it contains a very reactive aldehyde group at its 4' position that easily forms aldimines with primary and secondary amines and reacts with thiols. Most PLP is bound either to the enzymes that use it as a cofactor or to PLP carrier proteins, protected from the cellular environment but at the same time readily transferable to PLP-dependent apoenzymes. E. coli and its relatives synthesize PLP through the seven-step deoxyxylulose-5-phosphate (DXP)-dependent pathway. Other bacteria synthesize PLP in a single step, through a so-called DXP-independent pathway. Although the DXP-dependent pathway was the first to be revealed, the discovery of the widespread DXP-independent pathway determined a decline of interest in E. coli vitamin B₆ metabolism. In E. coli, as in most organisms, PLP can also be obtained from PL, PN, and PM, imported from the environment or recycled from protein turnover, via a salvage pathway. Our review deals with all aspects of vitamin B₆ metabolism in E. coli, from transcriptional to posttranslational regulation. A critical interpretation of results is presented, in particular, concerning the most obscure aspects of PLP homeostasis and delivery to PLP-dependent enzymes.

Characterization and functional insights into the Entamoeba histolytica pyridoxal kinase, an enzyme essential for its survival

Pyridoxal 5'-phosphate (PLP) is the active form of vitamin B₆ and a cofactor for more than 140 enzymes. This coenzyme plays a pivotal role in catalysis of various enzymatic reactions that are critical for the survival of organisms. Entamoeba histolytica depends on the uptake of pyridoxal (PL), a B₆ vitamer from the external environment which is then phosphorylated by pyridoxal kinase (EhPLK) to form PLP via the salvage pathway. E. histolytica cannot synthesise vitamin B₆de-novo, and also lacks pyridoxine 5'-phosphate oxidase, a salvage pathway enzyme required to produce PLP from pyridoxine phosphate (PNP) and pyridoxamine phosphate (PMP). Analysing the importance of PLK in E. histolytica, we have determined the high-resolution crystal structures of the dimeric pyridoxal kinase in apo, ADP-bound, and PLP-bound states. These structures provided a snapshot of the transition state and help in understanding the reaction mechanism in greater detail. The EhPLK structure significantly differed from the human homologue at its PLP binding site, and the phylogenetic study also revealed its divergence from human PLK. Further, gene regulation of EhPLK using sense and antisense RNA showed that any change in optimal level is harmful to the pathogen. Biochemical and in vivo studies unveiled EhPLK to be essential for this pathogen, while the molecular differences with human PLK structure can be exploited for the structure-guided design of EhPLK inhibitors.

Allosteric feedback inhibition of pyridoxine 5'-phosphate oxidase from Escherichia coli

In Escherichia coli, the synthesis of pyridoxal 5'-phosphate (PLP), the catalytically active form of vitamin B₆, takes place through the so-called deoxyxylulose 5-phosphate-dependent pathway, whose last step is pyridoxine 5'-phosphate (PNP) oxidation to PLP, catalyzed by the FMN-dependent enzyme PNP oxidase (PNPOx). This enzyme plays a pivotal role in controlling intracellular homeostasis and bioavailability of PLP. PNPOx has been proposed to undergo product inhibition resulting from PLP binding at the active site. PLP has also been reported to bind tightly at a secondary site, apparently without causing PNPOx inhibition. The possible location of this secondary site has been indicated by crystallographic studies as two symmetric surface pockets present on the PNPOx homodimer, but this site has never been verified by other experimental means. Here, we demonstrate, through kinetic measurements, that PLP inhibition is actually of a mixed-type nature and results from binding of this vitamer at an allosteric site. This interpretation was confirmed by the characterization of a mutated PNPOx form, in which substrate binding at the active site is heavily hampered but PLP binding is preserved. Structural and functional connections between the active site and the allosteric site were indicated by equilibrium binding experiments, which revealed different PLP-binding stoichiometries with WT and mutant PNPOx forms. These observations open up new horizons on the mechanisms that regulate E. coli PNPOx, which may have commonalities with the mechanisms regulating human PNPOx, whose crucial role in vitamin B₆ metabolism and epilepsy is well-known.

Structural and functional studies on Salmonella typhimurium pyridoxal kinase: the first structural evidence for the formation of Schiff base with the substrate

A large number of enzymes depend on the ubiquitous cofactor pyridoxal 5' phosphate (PLP) for their activity. Pyridoxal kinase (PLK) is the key enzyme involved in the synthesis of PLP from the three forms of vitamin B₆ via the salvage pathway. In the present work, we determined the unliganded structure of StPLK in a monoclinic form and its ternary complex with bound pyridoxal (PL), ADP and Mg²⁺ in two different tetragonal crystal forms (Form I and Form II). We found that, in the ternary complex structure of StPLK, the active site Lys233 forms a Schiff base linkage with the substrate (PL). Although formation of a Schiff base with the active site Lys229 was demonstrated in the Escherichia coli enzyme based on biochemical studies, the ternary complex of StPLK represents the first crystal structure where the Schiff bond formation has been observed. We also identified an additional site for PLP binding away from the active site in one of the ternary complexes (crystal Form I), suggesting a probable route for the product release. This is the first ternary complex structure where the modeled γ-phosphate of ATP is close enough to PL for the phosphorylation of the substrate. StPLK prefers PL over pyridoxamine as its substrate and follows a sequential mechanism of catalysis. Surface plasmon resonance studies suggest that StPLK interacts with apo-PLP-dependent enzymes with μm affinity supporting the earlier proposed direct transfer mechanism of PLP from PLK to PLP-dependent enzymes.

Human Cytosolic and Mitochondrial Serine Hydroxymethyltransferase Isoforms in Comparison: Full Kinetic Characterization and Substrate Inhibition Properties

Serine hydroxymethyltransferase (SHMT) catalyzes the reversible conversion of l-serine and tetrahydrofolate into glycine and 5,10-methylenetetrahydrofolate. This enzyme, which plays a pivotal role in one-carbon metabolism, is involved in cancer metabolic reprogramming and is a recognized target of chemotherapy intervention. In humans, two isoforms of the enzyme exist, which are commonly termed cytosolic SHMT1 and mitochondrial SHMT2. Considerable attention has been paid to the structural, mechanistic, and metabolic features of these isozymes. On the other hand, a detailed comparison of their catalytic and regulatory properties is missing, although this aspect seems to be considerably important, considering that SHMT1 and SHMT2 reside in different cellular compartments, where they play distinct roles in folate metabolism. Here we performed a full kinetic characterization of the serine hydroxymethyltransferase reaction catalyzed by SHMT1 and SHMT2, with a focus on pH dependence and substrate inhibition. Our investigation, which allowed the determination of all kinetic parameters of serine hydroxymethyltransferase forward and backward reactions, uncovered a previously unobserved substrate inhibition by l-serine and highlighted several interesting differences between SHMT1 and SHMT2. In particular, SHMT2 maintains a pronounced tetrahydrofolate substrate inhibition even at the alkaline pH characteristic of the mitochondrial matrix, whereas with SHMT1 this is almost abolished. At this pH, SHMT2 also shows a catalytic efficiency that is much higher than that of SHMT1. These observations suggest that such different properties represent an adaptation of the isoforms to the respective cellular environments and that substrate inhibition may be a form of regulation.

Biochemical data from the characterization of a new pathogenic mutation of human pyridoxine-5'-phosphate oxidase (PNPO)

PNPO deficiency is responsible of severe neonatal encephalopathy, responsive to pyridoxal-5′-phosphate (PLP) or pyridoxine. Recent studies widened the phenotype of this condition and detected new genetic variants on PNPO gene, whose pathogenetic role and clinical expression remain to be established. One of these mutations, Arg116Gln, is of particular interest because of its later onset of symptoms (beyond the first months of life) and its peculiar epileptic manifestations in patients. This protein variant was expressed as recombinant protein in E coli, purified to homogeneity, and characterized with respect to structural and kinetic properties, stability, binding constants of cofactor flavin mononucleotide (FMN) and product (PLP) in order to define the molecular and structural bases of its pathogenicity.

For interpretation and discussion of reported data, together with the description of clinical studies, refer to the article [1] (doi: 10.1016/j.ymgme.2017.08.003).

Isolation and characterization of the 5'-flanking region of the human PDXK gene

Pyridoxal kinase is a key enzyme for the biosynthesis of pyridoxal 5'-phosphate. Pyridoxal 5'-phosphate is the catalytically active form of vitamin B₆, and acts as a cofactor in >140 different enzyme reactions. It is still unknown how the kinase synthesis is regulated in the cells, and nothing has been reported about the gene promoter. In the present study, based on the bioinformatics analysis of the 5'-flanking region of the human PDXK gene, we cloned the promoter region by PCR. Through the construction of a series of luciferase expression vectors containing the human PDXK promoter region, we characterized the promoter in terms of its structure and function. The transcription start site is at 198bp upstream of the ATG translation initiation site. An important regulatory region is located at -665/-433bp upstream of the transcription start site. The promoter lacks the canonical TATA box, but contains three GC-boxes and one E-box. A deletion and mutation experiment revealed that the transcription factor Sp1 binding site C (-553/-543) is critical in maintaining the robust promoter activity. Knockdown of Sp1 by RNA interference and chromatin immunoprecipitation analysis further proved that the Sp1 is involved in the regulation of the PDXK gene expression.

Covalent inhibitors design and discovery

In the history of therapeutics, covalent drugs occupy a very distinct category. While representing a significant fraction of the drugs on the market, very few have been deliberately designed to interact covalently with their biological target. In this review, the prevalence of covalent drugs will first be briefly covered, followed by an introduction to their mechanisms of action and more detailed discussions of their discovery and the development of safe and efficient covalent enzyme inhibitors. All stages of a drug discovery program will be covered, from target considerations to lead optimization, strategies to tune reactivity and computational methods. The goal of this article is to provide an overview of the field and to outline good practices that are needed for the proper assessment and development of covalent inhibitors as well as a good understanding of the potential and limitations of current computational methods for the design of covalent drugs.

Identification and characterization of a pyridoxal 5'-phosphate phosphatase in the silkworm (Bombyx mori)

Vitamin B₆ comprises six interconvertible pyridine compounds, among which pyridoxal 5'-phosphate (PLP) is a coenzyme for over 140 enzymes. PLP is also a very reactive aldehyde. The most well established mechanism for maintaining low levels of free PLP is its dephosphorylation by phosphatases. A human PLP-specific phosphatase has been identified and characterized. However, very little is known about the phosphatase in other living organisms. In this study, a cDNA clone of putative PLP phosphatase was identified from B. mori and characterized. The cDNA encodes a polypeptide of 343 amino acid residues, and the recombinant enzyme purified from E. coli exhibited properties similar to that of human PLP phosphatase. B. mori has a single copy of the PLPP gene, which is located on 11th chromosome, spans a 5.7kb region and contains five exons and four introns. PLP phosphatase transcript was detected in every larva tissue except hemolymph, and was most highly represented in Malpighian tube. We further down-regulated the gene expression of the PLP phosphatase in 5th instar larvae with the RNA interference. However, no significant changes in the gene expression of PLP biosynthetic enzymes and composition of B₆ vitamers were detected as compared with the control.

Salmonella typhimurium PtsJ is a novel MocR-like transcriptional repressor involved in regulating the vitamin B6 salvage pathway

The vitamin B₆ salvage pathway, involving pyridoxine 5'-phosphate oxidase (PNPOx) and pyridoxal kinase (PLK), recycles B₆ vitamers from nutrients and protein turnover to produce pyridoxal 5'-phosphate (PLP), the catalytically active form of the vitamin. Regulation of this pathway, widespread in living organisms including humans and many bacteria, is very important to vitamin B₆ homeostasis but poorly understood. Although some information is available on the enzymatic regulation of PNPOx and PLK, little is known on their regulation at the transcriptional level. In the present work, we identified a new MocR-like regulator, PtsJ from Salmonella typhimurium, which controls the expression of the pdxK gene encoding one of the two PLKs expressed in this organism (PLK1). Analysis of pdxK expression in a ptsJ knockout strain demonstrated that PtsJ acts as a transcriptional repressor. This is the first case of a MocR-like regulator acting as repressor of its target gene. Expression and purification of PtsJ allowed a detailed characterisation of its effector and DNA-binding properties. PLP is the only B₆ vitamer acting as effector molecule for PtsJ. A DNA-binding region composed of four repeated nucleotide sequences is responsible for binding of PtsJ to its target promoter. Analysis of binding stoichiometry revealed that protein subunits/DNA molar ratio varies from 4 : 1 to 2 : 1, depending on the presence or absence of PLP. Structural characteristics of DNA transcriptional factor-binding sites suggest that PtsJ binds DNA according to a different model with respect to other characterised members of the MocR subgroup.

Mutations in PROSC Disrupt Cellular Pyridoxal Phosphate Homeostasis and Cause Vitamin-B6-Dependent Epilepsy

Pyridoxal 5'-phosphate (PLP), the active form of vitamin B₆, functions as a cofactor in humans for more than 140 enzymes, many of which are involved in neurotransmitter synthesis and degradation. A deficiency of PLP can present, therefore, as seizures and other symptoms that are treatable with PLP and/or pyridoxine. Deficiency of PLP in the brain can be caused by inborn errors affecting B₆ vitamer metabolism or by inactivation of PLP, which can occur when compounds accumulate as a result of inborn errors of other pathways or when small molecules are ingested. Whole-exome sequencing of two children from a consanguineous family with pyridoxine-dependent epilepsy revealed a homozygous nonsense mutation in proline synthetase co-transcribed homolog (bacterial), PROSC, which encodes a PLP-binding protein of hitherto unknown function. Subsequent sequencing of 29 unrelated indivduals with pyridoxine-responsive epilepsy identified four additional children with biallelic PROSC mutations. Pre-treatment cerebrospinal fluid samples showed low PLP concentrations and evidence of reduced activity of PLP-dependent enzymes. However, cultured fibroblasts showed excessive PLP accumulation. An E.coli mutant lacking the PROSC homolog (ΔYggS) is pyridoxine sensitive; complementation with human PROSC restored growth whereas hPROSC encoding p.Leu175Pro, p.Arg241Gln, and p.Ser78Ter did not. PLP, a highly reactive aldehyde, poses a problem for cells, which is how to supply enough PLP for apoenzymes while maintaining free PLP concentrations low enough to avoid unwanted reactions with other important cellular nucleophiles. Although the mechanism involved is not fully understood, our studies suggest that PROSC is involved in intracellular homeostatic regulation of PLP, supplying this cofactor to apoenzymes while minimizing any toxic side reactions.

Vitamin B6 metabolism in microbes and approaches for fermentative production

Vitamin B6 is a designation for the six vitamers pyridoxal, pyridoxine, pyridoxamine, pyridoxal 5'-phosphate (PLP), pyridoxine 5'-phosphate, and pyridoxamine. PLP, being the most important B6 vitamer, serves as a cofactor for many proteins and enzymes. In contrast to other organisms, animals and humans have to ingest vitamin B6 with their food. Several disorders are associated with vitamin B6 deficiency. Moreover, pharmaceuticals interfere with metabolism of the cofactor, which also results in vitamin B6 deficiency. Therefore, vitamin B6 is a valuable compound for the pharmaceutical and the food industry. Although vitamin B6 is currently chemically synthesized, there is considerable interest on the industrial side to shift from chemical processes to sustainable fermentation technologies. Here, we review recent findings regarding biosynthesis and homeostasis of vitamin B6 and describe the approaches that have been made in the past to develop microbial production processes. Moreover, we will describe novel routes for vitamin B6 biosynthesis and discuss their potential for engineering bacteria that overproduce the commercially valuable substance. We also highlight bottlenecks of the vitamin B6 biosynthetic pathways and propose strategies to circumvent these limitations.

Direct and indirect effects of RNA interference against pyridoxal kinase and pyridoxine 5'-phosphate oxidase genes in Bombyx mori

Vitamin B6 comprises six interconvertible pyridine compounds (vitamers), among which pyridoxal 5'-phosphate is a coenzyme involved in a high diversity of biochemical reactions. Humans and animals obtain B6 vitamers from diet, and synthesize pyridoxal 5'-phosphate by pyridoxal kinase and pyridoxine 5'-phosphate oxidase. Currently, little is known on how pyridoxal 5'-phosphate biosynthesis is regulated, and pyridoxal 5'-phosphate is supplied to meet their requirement in terms of cofactor. Bombyx mori is a large silk-secreting insect, in which protein metabolism is most active, and the vitamin B6 demand is high. In this study, we successfully down-regulated the gene expression of pyridoxal kinase and pyridoxine 5'-phosphate oxidase by body cavity injection of synthesized double-stranded small interfering RNA to 5th instar larvae of Bombyx mori, and analyzed the gene transcription levels of pyridoxal 5'-phosphate dependent enzymes, phosphoserine aminotransferase and glutamic-oxaloacetic transaminase. Results show that the gene expression of pyridoxal kinase and pyridoxine 5'-phosphate oxidase has a greater impact on the gene transcription of enzymes using pyridoxal 5'-phosphate as a cofactor in Bombyx mori. Our study suggests that pyridoxal 5'-phosphate biosynthesis and dynamic balance may be regulated by genetic networks.