A potential biotechnological process for the sustainable production of vitamin K1

The primary objective of this review is to propose an approach for the biosynthesis of phylloquinone (vitamin K₁) based upon its known sources, its role in photosynthesis and its biosynthetic pathway. The chemistry, health benefits, market, and industrial production of vitamin K are also summarized. Vitamin K compounds (K vitamers) are required for the normal function of at least 15 proteins involved in diverse physiological processes such as coagulation, tissue mineralization, inflammation, and neuroprotection. Vitamin K is essential for the prevention of Vitamin K Deficiency Bleeding (VKDB), especially in neonates. Increased vitamin K intake may also reduce the severity and/or risk of bone fracture, arterial calcification, inflammatory diseases, and cognitive decline. Consumers are increasingly favoring natural food and therapeutic products. However, the bulk of vitamin K products employed for both human and animal use are chemically synthesized. Biosynthesis of the menaquinones (vitamin K₂) has been extensively researched. However, published research on the biotechnological production of phylloquinone is restricted to a handful of available articles and patents. We have found that microalgae are more suitable than plant cell cultures for the biosynthesis of phylloquinone. Many algae are richer in vitamin K₁ than terrestrial plants, and algal cells are easier to manipulate. Vitamin K₁ can be efficiently recovered from the biomass using supercritical carbon dioxide extraction.     

Inability of men mutants of Escherichia coli to use trimethylamine-N-oxide as an electron acceptor

Abstract Mutants of Escherichia coli blocked in the biosynthesis of menaquinone were unable to use trimethylamine- N -oxide as an electron acceptor in complex medium containing glucose. Trimethylamine- N -oxide reduction and the consequent in-crease in growth could be restored in a menC mutant by either o -succinylbenzoic acid (OSB) or 1,4-dihydroxy-2-naphthoic acid (DHNA). In the case of a menB mutant, growth could not be restored by OSB; but addition of DHNA resulted in the restoration of growth to the full extent. These results are consistent with the metabolic blocks in the respective men mutants.     

Structural and functional insights into human vitamin K epoxide reductase and vitamin K epoxide reductase-like1

Abstract

Human vitamin K epoxide reductase (hVKOR) is a small integral membrane protein involved in recycling vitamin K. hVKOR produces vitamin K hydroquinone, a crucial cofactor for γ-glutamyl carboxylation of vitamin K dependent proteins, which are necessary for blood coagulation. Because of this, hVKOR is the target of a common anticoagulant, warfarin. Spurred by the identification of the hVKOR gene less than a decade ago, there have been a number of new insights related to this protein. Nonetheless, there are a number of key issues that have not been resolved; such as where warfarin binds hVKOR, or if human VKOR shares the topology of the structurally characterized but distantly related prokaryotic VKOR. The pharmacogenetics and single nucleotide polymorphisms of hVKOR used in personalized medicine strategies for warfarin dosing should be carefully considered to inform the debate. The biochemical and cell biological evidence suggests that hVKOR has a distinct fold from its ancestral protein, though the controversy will likely remain until structural studies of hVKOR are accomplished. Resolving these issues should impact development of new anticoagulants. The paralogous human protein, VKOR-like1 (VKORL1) was recently shown to also participate in vitamin K recycling. VKORL1 was also recently characterized and assigned a functional role as a housekeeping protein involved in redox homeostasis and oxidative stress with a potential role in cancer regulation. As the physiological interplay between these two human paralogs emerge, the impacts could be significant in a number of diverse fields from coagulation to cancer.     

Determination of the warfarin inhibition constant Ki for vitamin K 2,3-epoxide reductase complex subunit-1 (VKORC1) using an in vitro DTT-driven assay

Background

Warfarin directly inhibits vitamin K 2,3-epoxide reductase (VKOR) enzymes. Since the early 1970s, warfarin inhibition of vitamin K 2,3-epoxide reductase complex subunit 1 (VKORC1), an essential enzyme for proper function of blood coagulation in higher vertebrates, has been studied using an in vitro dithiothreitol (DTT) driven enzymatic assay. However, various studies based on this assay have reported warfarin dose–response data, usually summarized as half-maximal inhibitory concentration (IC₅₀), that vary over orders of magnitude and reflect the broad range of conditions used to obtain VKOR assay data.

Methods

We standardized the implementation of the DTT-driven VKOR activity assay to measure enzymatic Michaelis constants (K_m) and warfarin IC₅₀ for human VKORC1. A data transformation is defined, based on the previously confirmed bi bi ping-pong mechanism for VKORC1, that relates assay condition-dependent IC₅₀ to condition-independent K_i.

Results

Determination of the warfarin K_i specifically depends on measuring both substrate concentrations, both Michaelis constants for the VKORC1 enzyme, and pH in the assay.

Conclusion

The K_i is not equal to the IC₅₀ value directly measured using the DTT-driven VKOR assay.

General significance

In contrast to warfarin IC₅₀ values determined in previous studies, warfarin inhibition expressed as K_i can now be compared between studies, even when the specific DTT-driven VKOR assay conditions differ. This implies that warfarin inhibition reported for wild-type and variant VKORC1 enzymes from previous reports should be reassessed and new determinations of K_i are required to accurately report and compare in vitro warfarin inhibition results.     

Vitamin K, 2,3-Epoxide And Quinone Reduction: Mechanism And Inhibition

The chemical and enzymatic pathways of vitamin K₁ epoxide and quinone reduction have been investigated. The reduction of the epoxide by thiols is known to involve a thiol-adduct and a hydroxy vitamin K enolate intermediate which eliminates water to yield the quinone. Sodium borohydride treatment resulted in carbonyl reduction generating relatively stable compounds that did not proceed to quinone in the presence of base. NAD(P)H:quinone oxidoreductase (DT-diaphorase. E.C. I.6.99.2) reduction of vitamin K to the hydroquinone was a significant process in intact microsomes. but 1/5th the rate of the dithiothreitol (DTT)-dependent reduction. No evidence was found for DT-diaphorase catalyzed reduction of vitamin K₁ epoxide, nor was it capable of mediating transfer of electrons from NADH to the microsomal epoxide reducing enzyme. Purified diaphorase reduced detergent- solubilized vitamin K, 10^?5 as rapidly as it reduced dichlorophenylindophenol(DCPIP). Reduction of 10 μM vitamin K, by200 μM NADH was not inhibited by 10μM dicoumarol. whereas DCPIP reduction was fully inhibited. In contrast to vitamin K, (menadione). vitamin K₁ (phylloquinone) did not stimulate microsomal NADPH consumption in the presence or absence of dicoumarol. DTT-dependent vitamin K epoxide reduction and vitamin K reduction were shown to be mutually inhibitory reactions. suggesting that both occur at the same enzymatic site. On this basis, a mechanism for reduction of the quinone by thiols is proposed. Both the DTT-dependent reduction of vitamin K₁ epoxide and quinone. and the reduction of DCPIP by purified DT-diaphorase were inhibited by dicoumarol, warfarin. lapachol. and sulphaquinoxaline     

中国云南汉族群体VKORC1基因多态性研究

目的：探讨云南汉族人群维生素K环氧化物还原酶亚单位1（VKORC1 ）基因多态性,并与国内外群体进行比较。方法：采集280云南汉族心瓣膜置换术病人外周血,获得基因组DNA,用PCR-RFLP 方法分析VKORC1-1639G/A,1173C/T,3730A/G 的基因多态性。结果：对于VKORC1-1639G/A,共检出222 (79.3%)名AA纯合子,8(2.8%)名GG纯合子,50(17.9%)名AG杂合子;对于VKORC1-1173C/T,检出224 (80.0%) 名纯合子TT,56 (20.0%)名杂合子CT,未检出CC 基因型;对于VKORC1 3730 A/G,共检出30(10.7%)名AA 基因型,205 (73.2%)名GG 基因型,45 (16.1%)名AG 基因型。与不同群体相比,各位点差别不一。结论：与其他群体相比,云南汉族人群VKORC1-1639G/A,1173C/T,3730A/G 基因位点具有自己的遗传多态性,其基因多态性在临床药物应用（如华法林）治疗中具有非常重要的意义。     

Temporal Variation in the Effects of Warfarin on the Vitamin K Cycle

In this in vivo study, the time-dependent effect of oral sodium warfarin was studied in male rats synchronized under a 12-hr light-dark cycle (light 0600–1800). Groups of 5 animals received an oral dose of 500 Mg/kg of warfarin or saline at 0600 or 1800 and 1 mg/kg of vitamin K 8 hr later and the rats were sacrificed 240 min after vitamin K administration. The activities of the vitamin K reductase and vitamin K epoxide reductase were measured indirectly by determining the content of vitamin K, and vitamin K epoxide reductase in the plasma and liver. The data obtained in control rats indicated that vitamin K and vitamin K 2,3 epoxide concentrations in plasma and liver were higher (P < 0.05) at 1800 than at 0600. Warfarin had a greater (P < 0.05) inhibitory effect on the vitamin K and vitamin K-epoxide reductases at 0600 compared to 1800; plasma levels of S- and R-warfarin did not vary with time of administration. The findings suggest that the activity of both reductases under control conditions, and the warfarin-induced inhibition of these enzymes varied depending on the time of drug administration.     

Tentoxin An uncompetitive inhibitor of lettuce chloroplast coupling factor 1

The interaction of tentoxin $\text{[cyclo}\text{(-}\text{l}\text{-leucyl}\text{-N-}\text{methyl-(Z)-dehydrophenyl-analyl-glycyl}\text{-N-}\text{methyl-}\text{l}\text{-alanyl-)}\text{]}$ with solubilized lettuce chloroplast coupling factor 1 was characterized by direct binding studies, measurement of the time course of ATPase inhibition, and steady-state enzyme kinetics. Neither substrates, products or Ca²⁺ competed with the tentoxin binding site, nor did they induce any large change in tentoxin affinity. The inhibition of lettuce chloroplast coupling factor 1 ATPase was found to be the time dependent, and at equilibrium the affinities estimated by equilibrium ultrafiltration and enzyme inhibition were similar (1.8 · 10⁸M^?1). The steady-state kinetics best fit an uncompetitive pattern suggesting that the inhibited steps follow an irreversible step occurring after ATP binding.     

Structure of thermoplasmaquinone from Thermoplasma acidophilum

Abstract The structure of the methyl-substituted menaquinone (designated thermoplasmaquinone) from the extremely thermophilic and acidophilic archaebacterium Thermoplasma acidophilum was investigated by mass spectrometry and proton nuclear magnetic resonance spectrometry. The results of the present study show that the novel quinone from T. acidophilum corresponds to 2,[5 or 8]-dimethyl-3-heptaprenyl-1,4-naphthoquinone.     

High-pressure liquid chromatographic-reductive electrochemical detection analysis of serum trans-phylloquinone

A sensitive method for the determination of human serum trans-phylloquinone levels has been developed. Serum samples were extracted with hexane and subjected to preliminary separation on a silica semipreparative HPLC column with an 80% recovery as determined by the addition of [³H]phylloquinone. The portion of the eluate containing trans-phylloquinone was dried and injected into a μBondapak C-18 analytical HPLC column, and the concentration of the vitamin was determined by reductive electrochemical detection utilizing a glassy carbon electrode and and $\text{Ag}\text{AgCl}$ reference electrode. The presumed vitamin peak was confirmed as trans-phylloquinone by rechromatography at different HPLC conditions, hydrodynamic voltamography, and photodegradation. As little as 300 pg/ml rans-phylloquinone could be detected, and normal human serum concentrations were found to be in the range of 1 ng/ml.