High impact information on PLP

• This constitutes an essential step in the synthesis of pyridoxal 5'-phosphate (PLP), the active form of vitamin B6, a cofactor for over 140 enzymes [1].
• The gene product was a homodimer with the subunit Mr of 44,439, contained 1 mol of PLP as a cofactor per mol of subunit, and catalyzed the release of Se, SO2, and S from L-selenocysteine, L-cysteine sulfinic acid, and L-cysteine, respectively, to yield L-alanine; the reactivity of the substrates decreased in this order [2].
• Addition of AcP to the enzyme induced a slight decrease in the fluorescence of the PLP probe in the presence of 2 M NaCl and 4 mM MgCl2 but a single exponential increase in the presence of 16 mM NaCl and 4 mM MgCl2 [3].
• Lys-497 was concluded to be the binding site of PLP, as pyridoxyl-Lys was identified at the corresponding position [4].
• Limited proteolysis of the enzyme modified with [3H]PLP by trypsin suggests that PLP specifically modifies the lysine residue located in the 16-kDa fragment of the enzyme cleaved by trypsin [5].

Biological context of PLP

• These results suggested that PLP binds to a specific lysine residue in the nucleotide-binding site or a region in its vicinity and inhibits the substrate binding or phosphorylation step of (H+ + K+)-ATPase [5].
• Binding of new PLP analogs to the catalytic domain of GABA transaminase [6].
• This PLP-dependent enzyme is proposed to catalyze the final step in the metabolic activation of cisplatin [7].
• Under the prescribed conditions of hydrolysis, PLP forms its phenylhydrazone and is released from the protein and hydrolyzed to the phenylhydrazone of pyridoxal, which shows a typical fragmentation in direct electron impact and in gas chromatography-mass spectrometry after silylation [8].

Anatomical context of PLP

• Skeletal muscle and liver PLP content were 35% lower than initial by 6 hr postmortem (P less than 0.01) [9].
• PEDV antigen was consistently detected in the PLP (4% paraformaldehyde, 100 mM L-lysine dihydrochloride, 10 mM sodium m-periodate in phosphate-buffered saline)-fixed PEDV-infected Vero cells or formalin-fixed, paraffin-embedded intestinal tissues from piglets naturally infected with PEDV [10].

Associations of PLP with chemical compounds

• Pig gastric membrane vesicles enriched in (H+ + K+)-ATPase were covalently modified with pyridoxal 5'-phosphate (PLP) [5].
• RR spectra of the erythro-beta-hydroxy-DL-aspartate complex, representing the p-quinoid enzyme intermediate, as well as of AlIII complexes of PLP Schiff bases with phenylalanine and tyrosine ethyl ester have been obtained via the coherent anti-Stokes Raman scattering technique, and partially assigned [11].
• Treatment of the enzyme with phenylhydrazine (PH) according to a procedure developed for analysis of quinoproteins gave products which were identified as the hydrazone of pyridoxal phosphate (PLP) and the C(5)-hydrazone of pyrroloquinoline quinone (PQQ) [12].
• This behavior contrasts that of free pyridoxal phosphate (PLP) and pyridoxamine phosphate (PMP) in solution, where the dependence of the same infrared band intensity with pH can be correlated to the known pK values for the 5'-phosphate ester in solution [13].
• These findings suggest that tryptophan 248 interacts closely with PLP and plays an important role in the catalytic reaction [14].

Other interactions of PLP

• Taken together, these findings indicate that recombinant pig kidney DDC has two active-site PLP molecules and therefore displays structural characteristics typical of PLP-dependent homodimeric enzymes [15].
• Moreover, binding profiles of both enzymes to immobilized PK were altered by excess amount of PLP [16].
• These results are taken as evidence that in the active site of mitochondrial aspartate aminotransferase the 5'-phosphate group of PLP remains mostly dianionic even at a pH near 5 [13].

Analytical, diagnostic and therapeutic context of PLP

• The peptides labeled with radioactive PLP could be released from the gastric membrane vesicles quantitatively by chymotrypsin treatment, and two peptides were purified by high performance liquid chromatographies [4].
• Since no chemical shift changes were observed in pH titrations of the PMP forms (lacking an ionizable internal aldimine) of this isozyme, the Schiff base between PLP and Lys-258 at the active site is the most likely candidate for the ionizing group influencing the phosphorus chemical shift in this enzyme [13].
• Dopa decarboxylase from pig kidney is a pyridoxal-5'-phosphate (PLP) dependent enzyme that displays positive circular dichroism (CD) relative to the coenzyme absorption bands at 335 and 420 nm, which are characteristic of an asymmetrically bound coenzyme [17].
• After tryptic digestion of the enzyme modified with PLP, a radioactive peptide absorbing at 210 nm was isolated by reverse-phase HPLC [18].
• Inactivation of [3H] PLP-reconstituted GABA aminotransferase with 2 followed by gel filtration then base denaturation released all of the radioactivity as a mixture of PLP, 3, and 4 [19].

References