Phenolic Metabolism Research Articles

Bioavailability of Food Polyphenols: Current State of Knowledge

(Poly)phenols, including flavonoids, phenolic acids, and tannins, are a diverse class of compounds found in plant-based foods and beverages. Their bioavailability has been extensively described and detailed metabolic pathways elucidated. Although some parent (poly)phenols are absorbed intact in the small intestine, most pass to the colon where they are extensively catabolized and their microbial products absorbed into the circulation. The sum of the metabolites absorbed can reach almost 100% in some cases and in some individuals. In recent years, there have been three major areas of advancement: (a) comprehensive and systematic reviews have brought together bioavailability data, including detailed metabolic pathways in humans, and quantitative estimates of absorption and excretion; (b) the action and importance of the gut microbiota in (poly)phenol metabolism have been better defined and our understanding of the important role of the microbiota in intra- and interindividual variation has greatly expanded; and (c) strategies to improve (poly)phenol bioavailability such as encapsulation employing various nanoformulations or cyclodextrins have been developed.

Integrated metabolomics and transcriptomics reveal the role of calcium sugar alcohol in the regulation of phenolic acid biosynthesis in Torreya grandis nuts

BackgroundTorreya grandis, a prominent tree species of the autochthonous subtropical region of China, possesses a drupe-like fruit containing a nut that is rich in nutrients and bioactive compounds. However, the effect of calcium (Ca2+) sugar alcohol (CSA), a newly developed chelated Ca2+-fertilizer, on the secondary metabolism of phenolics in T. grandis nuts is largely unknown, for which transcriptomic and metabolomic analysis was carried out.ResultsTranscriptome sequencing detected 47,064 transcripts, and several phenolic acid biosynthesis pathway-related genes were identified. Correlation analysis showed that the four transcription factors, TgWRKY1, TgAP2-1, TgAP2-3, and TgAP2-4, were positively associated with the accumulation of phenolic acids. Furthermore, the binding of TgAP2-1 to the TgHCT promoter was confirmed using yeast one hybrid and dual-luciferase assays. Furthermore, the expression of TgHCT in Nicotiana enhanced the total flavonoid content.ConclusionsOur results indicated that a new regulatory module, Ca2+–AP2–HCT, involved in the regulation of phenolic acid biosynthesis was revealed, expanding the understanding of the role of Ca2+ fertilizers in plant secondary metabolism.

Utilizing physiologies, transcriptomics, and metabolomics to unravel key genes and metabolites of Salvia miltiorrhiza Bge. seedlings in response to drought stress.

Drought stress inhibits Salvia miltiorrhiza Bunge (S. miltiorrhiza) seedling growth and yield. Here, we studied the effects of drought stress on the different parts of S. miltiorrhiza seedlings through physiological, transcriptomic, and metabolomics analyses, and identified key genes and metabolites related to drought tolerance. Physiological analysis showed that drought stress increased the accumulation of hydrogen peroxide (H2O2), enhanced the activity of peroxidase (POD), decreased the activity of catalase (CAT) and the contents of chlorophyll b and total chlorophyll, reduced the degree of photosynthesis, enhanced oxidative damage in S. miltiorrhiza seedlings, and inhibited the growth of S. miltiorrhiza plants. Transcriptome analyses revealed 383 genes encoding transcription factors and 80 genes encoding plant hormones as hypothetical regulators of drought resistance in S. miltiorrhiza plants. Moreover, differentially expressed genes (DEGs) and differentially expressed metabolites (DEMs) are involved in a variety of biological processes, such as proline and glycine betaine metabolism, and biosynthesis of tanshinones and phenolic acids. Additionally, it has barely been reported that the AHL gene family may be involved in regulating the neocryptotanshinone biosynthesis. In conclusion, our results suggest that drought stress inhibits S. miltiorrhiza seedling growth by enhancing membrane lipid peroxidation, attenuating the antioxidant system, photosynthesis, and regulating proline and glycine betaine metabolism, transcription factors and plant hormones, and tanshinones and phenolic acid metabolism pathways. This study provides new insights into the complex mechanisms by which S. miltiorrhiza responds to drought stress.

Combination transcriptomic and metabolomic reveal deterioration of the blue honeysuckle (Lonicera caerulea L.) fruit and candidate genes regulating metabolism in the post-harvest stage

Blue honeysuckle, a new berry with high nutritional value, possesses typical berry postharvest properties, including extreme perishability, rapid quality loss, and high sensitivity to microbial infections. At present, the underlying mechanisms of postharvest quality deterioration, senescence, and low-temperature regulation remain largely unknown. This study aimed to elucidate the metabolic shifts and genetic regulation underlying the preservation or deterioration of blue honeysuckle during storage at room temperature (25 °C) and low temperature (4 °C). Storage at 4 °C inhibited fruit decay and preserved better visual quality, weight, firmness, and total soluble solid and acid contents. We identified 24 key differentially accumulated metabolites that specifically changed during the qualitative shift at room temperature and were effectively regulated by 4 °C. Commonly associated metabolites, sorbitol, succinic acid, malic acid, naringenin, pinobanksin, and taxifolin, characterize the deterioration of blue honeysuckle. These metabolites were integrated with transcriptomic data for weighted correlation network analysis (WGCNA). Regulatory networks were used for the identification of key genes and transcription factors (TFs) influencing sugar, organic acid, flavonoid, and phenolic acid metabolism during storage. The findings provide insight into metabolic regulation and the improvement of flavor in postharvest blue honeysuckle fruit.

Combined physiological, biochemical, and multi-omic analyses provide insight into the cause of differential browning in early and late harvested fresh-cut yams

Tissue browning reduces the cosmetic quality of fresh-cut yams and poses a marketing problem. The degree of browning of fresh-cut yams varies depending on when they are harvested. In this study, transcriptomic and metabolomic analyses were conducted in yams harvested in September (DHPS) and October (DHPO) to determine the mechanisms responsible for the browning of fresh-cut yams. Results showed that the browning index, total phenol and lignin content, polyphenol oxidase (PPO), peroxidase (POD), phenylalanine ammonia-lyase (PAL), 4-coumarate: CoA Ligase(4CL), and cinnamic acid-4-hydroxylase(C4H) activity in fresh-cut DHPO yams were lower than they were in fresh-cut DHPS yams. Flavonoids and catalase (CAT) activity remained consistently higher during storage in DHPO yams than in DHPS yams. The browning of fresh-cut DHPO yams was mitigated by the regulation of the expression of genes and the abundance of metabolites associated with phenolic metabolism, phytohormones, and signal transduction, as well as sucrose and starch metabolism. The level of browning enzyme activity in DHPO yams was significantly lower than it was in DHPS yams. Our study provides a basis for the selection of optimum harvest date for yams that will undergo fresh-cut processing.

Riboflavin improves postharvest cold tolerance in zucchini fruit inducing non-enzymatic antioxidant response and phenolic metabolism

The storage of zucchini fruit at low temperatures during postharvest induces a physiological disorder called chilling injury that drastically reduces fruit quality and shelf life. The phytohormone abscisic acid (ABA) is involved in the acquisition of cold tolerance in zucchini fruit, being the riboflavin pathway one of the most differentially induced with ABA treatment. Thus, the aim of this work was to elucidate the involvement of riboflavin in quality maintenance of zucchini fruit during postharvest cold storage. After testing different concentrations of exogenous riboflavin, 0.5 mM showed the best results. Riboflavin treatment reduced H2O2 content, but the enzymatic antioxidant defense did not change significantly. This response is due to a rise of non-enzymatic antioxidant defense, by accumulating metabolites like ascorbate and carotenoids, as well as inducing phenolic metabolism. The application of this vitamin enhanced the phenolic and flavonoid content in fruit, concomitant with an induction of PAL and C4H activities and an inhibition of PPO activity. This enhancement of the phenylpropanoid pathway resulted in high vanillic acid and quercetin levels at first day of cold storage. The induction of numerous antioxidant compounds and abscisic acid by riboflavin treatment at short-term postharvest period could be responsible for the lack of chilling injuries in zucchini fruit. Therefore, riboflavin could be successfully implemented in the food industry as an alternative to physical or chemical treatments, due to it is an innocuous additive with good water solubility and low cost, as it prolongs the shelf-life of zucchini fruit and increases its nutraceutical properties.

Methyl jasmonate alleviates the husk browning and regulates expression of genes related to phenolic metabolism of pomegranate fruit

Pomegranate is sensitive to low temperature and is susceptible to chilling injury (CI), resulting in husk browning. The effects of Methyl jasmonate (MeJA), hot water treatment (HWT), and control treatments on the quality of pomegranate fruit during low temperature storage were investigated. The results showed that MeJA and HWT treatments could effectively inhibit the increase of browning index, color difference, relative conductivity, polyphenol oxidase (PPO) and peroxidase (POD) activities, maintain phenolic substances and the activity of phenylalanine ammonia-lyase (PAL). The browning index of MeJA treatment was 55.42 % lower than control treatment on the 70th day, the relative conductivity and MDA content were 24.32 % and 51.67 % lower than control treatment, respectively. Furthermore, MeJA treatment delayed the increase of PgPPO and PgPOD gene expression levels, upregulated the expression levels of PgPAL gene. Overall, MeJA treatment could improve antioxidant capacities, alleviate CI by regulating phenolic metabolism and gene expression levels.

Perspective on the Coevolutionary Role of Host and Gut Microbiota in Polyphenol Health Effects: Metabotypes and Precision Health.

"Personalized nutrition" aims to establish nutritional strategies to improve health outcomes for non-responders. However, it is utopian since most people share similar nutritional requirements. "Precision health," encompassing lifestyles, may be more fitting. Dietary (poly)phenols are "healthy" but non-nutritional molecules (thus, we can live without them). The gut microbiota influences (poly)phenol effects, producing metabolites with different activity than their precursors. Furthermore, producing distinctive metabolites, like urolithins, lunularin, and equol, leads to the term "polyphenol-related gut microbiota metabotypes," grouping individuals based on a genuine microbial metabolism of ellagic acid, resveratrol, and isoflavones, respectively. Additionally, (poly)phenols exert prebiotic-like effects through their antimicrobial activities, typically reducing microbial diversity and modulating microbiota functionality by impacting its composition and transcriptomics. Since the gut microbiota perceives (poly)phenols as a threat, (poly)phenol effects are mostly a consequence of microbiota adaptation through differential (poly)phenol metabolism (e.g., distinctive reductions, dehydroxylations, etc.). This viewpoint is less prosaic than considering (poly)phenols as essential nutritional players in human health, yet underscores their health significance in a coevolutionary partnership with the gut microbiota. In the perspective on the gut microbiota and (poly)phenols interplay, microbiota metabotypes could arbiter health effects. An innovative aspect is also emphasized: modulating the interacting microbial networks without altering the composition.

Mutual Interactions of Silymarin and Colon Microbiota in Healthy Young and Healthy Elder Subjects.

This multi-omic study investigates the bidirectional interactions between gut microbiota and silymarin metabolism, highlighting the differential effects across various age groups. Silymarin, the extract from Silybum marianum (milk thistle), is commonly used for its hepatoprotective effects. An in vitro fermentation colon model was used with microbiota from 20 stool samples obtained from healthy donors divided into two age groups. A combination of three analytical advanced techniques, namely proton nuclear magnetic resonance (1H NMR), next-generation sequencing (NGS), and liquid chromatography-mass spectrometry (LC-MS) was used to determine silymarin microbial metabolites over 24h, overall metabolome, and microbiota composition. Silymarin at a low diet-relevant dose of 50µgmL-1 significantly altered gut microbiota metabolism, reducing short-chain fatty acid (acetate, butyrate, propionate) production, glucose utilization, and increasing alpha-diversity. Notably, the study reveals age-related differences in silymarin catabolism. Healthy elderly donors (70-80 years) exhibited a significant increase in a specific catabolite associated with Oscillibacter sp., whereas healthy young donors (12-45 years) showed a faster breakdown of silymarin components, particularly isosilybin B, which is associated with higher abundance of Faecalibacterium and Erysipelotrichaceae UCG-003. This study provides insights into microbiome functionality in metabolizing dietary flavonolignans, highlighting implications for age-specific nutritional strategies, and advancing our understanding of dietary (poly)phenol metabolism.

Agronomic Evaluation and Chemical Characterization of Salvia lavandulifolia Vahl. over 3 Consecutive Years Cultivated Under Harsh Climatic Conditions in Southeast Spain.

The cultivation of Salvia lavandulifolia, Spanish sage, makes an important contribution to the economy of many rural areas in Southeastern Spain. This aromatic plant species is characterized by high intraspecific variability, which makes the selection process for the establishment of homogeneous crops difficult. Additionally, imminent climate change threatens to reduce its production, especially when cultivated in drylands. Therefore, to guarantee the continued production of this type of sage, it is essential to study its agronomic behavior and production quality. For this, clones from four ecotypes were cultivated for three years, assessing changes in their biomass production, essential oil yield and quality, and phenolic fraction, as well as the corresponding antioxidant activity. The results suggest that essential oil yield is genetically predetermined, greater biomass not being associated with higher quantities of essential oil. Weather conditions affected both essential oil and phenolic fraction secondary metabolism. Under very harsh conditions, Spanish sage produces higher concentrations of camphor and 1,-8-cineole along with luteolin-7-O-glucoside, and lithospermic, rosmarinic, and salvianolic A acids in its phenolic fraction. The synthesis of these components helps the species to withstand the hot and dry conditions typical of southeast Spain.

Impact of chlorocholine chloride on phenolic metabolism in in vitro cultures of Gardenia jasminoides (Variegata and Ellis)

Impact of chlorocholine chloride on phenolic metabolism in in vitro cultures of Gardenia jasminoides (Variegata and Ellis)

Methyl Jasmonate Application Downregulates Drupelet Reversion and Enhances Phenolic Biosynthesis and Antioxidant Potential of Blackberries

Blackberry plants were sprayed with methyl jasmonate (MJ 0, 1, 2 or 3 mmol L−1), 2 weeks before tentative harvest maturity, to evaluate its influence on red drupelet reversion (RDR), antioxidant capacity and postharvest quality during cold storage up to 12 days. MJ significantly reduced RDR and weight loss while maintaining higher anthocyanins and flavonoids during cold storage for 12 days. MJ application upregulated phenolic metabolism by maintaining higher phenylalanine ammonia lyase activity, and showed higher total antioxidants, ascorbic acid, and glutathione content. MJ-treated blackberries displayed higher activities of superoxide dismutase, catalase, ascorbate peroxidase, monodehydroascorbate reductase, dehydroascorbate reductase and glutathione reductase enzymes, than control for 12 days of cold storage. Moreover, MJ-treated fruit suppressed the production of hydrogen peroxide radicals and malondialdehyde with lower activities of polyphenol oxidase and lipoxygenase enzymes. In conclusion, preharvest application of MJ has the potential to reduce RDR, improve antioxidant capacity and maintain fruit quality of cold stored blackberries.

Differential Responses of Phenolics and Lignin Metabolism to Excess Iron and Zinc in Monocot and Dicot Roots Treated by Silicon

Differential Responses of Phenolics and Lignin Metabolism to Excess Iron and Zinc in Monocot and Dicot Roots Treated by Silicon

Inoculation with Jeotgalicoccus sp. improves nutritional quality and biological value of Eruca sativa by enhancing amino acid and phenolic metabolism and increasing mineral uptake, unsaturated fatty acids, vitamins, and antioxidants.

Plant growth-promoting bacteria (PGPB) are considered a promising tool for triggering the synthesis of bioactive compounds in plants and to produce healthy foods. This study aimed to demonstrate the impact of PGPB on the growth, accumulation of primary and secondary metabolites, biological activities, and nutritional qualities of Eruca sativa (arugula), a key leafy vegetable worldwide. To this end, Jeotgalicoccus sp. (JW0823), was isolated and identified by using partial 16S rDNA-based identification and phylogenetic analysis. The findings revealed that JW0823 significantly boosted plant biomass production by about 45% (P<0.05) and enhanced pigment contents by 47.5% to 83.8%. JW0823-treated plants showed remarkable improvements in their proximate composition and vitamin contents, with vitamin E levels increasing by 161.5%. JW0823 induced the accumulation of bioactive metabolites including antioxidants, vitamins, unsaturated fatty acids, and essential amino acids, thereby improving the nutritional qualities of treated plants. An increase in the amounts of amino acids was recorded, with isoleucine showing the highest increase of 270.2%. This was accompanied by increased activity of the key enzymes involved in amino acid biosynthesis, including glutamine synthase, dihydrodipicolinate synthase, cystathionine γ-synthase, and phenylalanine ammonia-lyase enzymes. Consequently, the total antioxidant and antidiabetic activities of the inoculated plants were enhanced. Additionally, JW0823 improved antimicrobial activity against several pathogenic microorganisms. Overall, the JW0823 treatment is a highly promising method for enhancing the health-promoting properties and biological characteristics of E. sativa, making it a valuable tool for improving the quality of this important leafy vegetable.

Preharvest methyl jasmonate application delays cell wall degradation and upregulates phenolic metabolism and antioxidant activities in cold stored raspberries

The effects of preharvest methyl jasmonate (MeJA) spray application on the physicochemical quality, metabolism of phenolics, and cell wall components in raspberries were investigated during a 10-day cold storage period. MeJA spray reduced firmness loss, decay incidence, and weight loss, while maintained higher levels of soluble solids content, ascorbic acid, anthocyanins and flavonoids in raspberries. Furthermore, MeJA application resulted in increased total pectin and protopectin levels, as well as lowered water-soluble pectin, and activities of pectin methyl esterase, polygalacturonase and cellulase enzymes. Additionally, MeJA treatment upregulated the phenylpropanoid pathway, leading to higher endogenous phenolics and activities of phenylalanine-ammonia lyase and shikimate dehydrogenase. In conclusion, preharvest MeJA spray application could be adopted to enhance the storage potential of cold-stored raspberries for 10 days by maintaining higher firmness, assuring better physicochemical quality, and increasing phenolic metabolism, while reducing cell wall hydrolysis.

In vivo detection of endogenous toxic phenolic compounds of intestine

Phenol and p-cresol are two common toxic small molecules related to various diseases. Existing reports confirmed that high L-tyrosine in the daily diet can increase the concentration of phenolic compounds in blood and urine. L-tyrosine is a common component of protein-rich foods. Some anaerobic bacteria in the gut can convert non-toxic l-tyrosine into these two toxic phenolic compounds, phenol and p-cresol. Existing methods have been constructed for measuring the concentration of phenolic compound in feces. However, there is still a lack of direct visual evidence to measure the phenolic compounds in the intestine. In this study, we aimed to construct a whole-cell biosensor for phenolic compounds detection based on the dmpR, the regulator from the phenol metabolism cluster. The commensal bacterium Citrobacter amalonaticus PS01 was selected and used as the chassis. Compared with the biosensor based on ECN1917, the biosensor PS01[dmpR] could better implant into the mouse gut through gavage and showed a higher sensitive to phenolic compound. And the concentration of phenolic compounds in the intestines could be observed with the help of in vivo imaging system using PS01[dmpR]. This paper demonstrated endogenous phenol synthesis in the gut and the strategy of using commensal bacteria to construct whole-cell biosensors for detecting small molecule compounds in the intestines.

Sex-Linked Changes in Biotransformation of Phenol in Brook Trout (Salvelinus fontinalis) over an Annual Reproductive Cycle

The microsomal metabolism of phenol (11 °C) over an annual reproductive cycle from June to December was studied using fall spawning adult brook trout (Salvelinus fontinalis). Hepatic microsomes were isolated from three male and three female fish each month. Incubations were optimized for time, cofactor concentration, pH, and microsomal protein concentration. The formation of phase I ring-hydroxylation metabolites, i.e., hydroquinone (HQ) and catechol (CAT), was quantified by HPLC with dual-channel electrochemical detection. Sample preparation and chromatographic conditions were optimized to achieve the separation and sensitivity required for the analysis of these labile products. Biotransformation of phenol over a range of substrate concentrations (1 to 150 mM) was quantified for the calculation of Michaelis–Menten constants (Km and Vmax) for each month. Results indicate a nearly equal production of HQ and CAT among males and females in late June. At the peak of maturity in October, there was an approximate ten-fold greater production of ring-hydroxylation metabolites noted in females in comparison with males on a total liver basis. In vitro phase II biotransformation of phenol glucuronidation was assessed by determining the Michaelis–Menten constants (Km, Vmax) using brook trout hepatic microsomes over a range of substrate concentrations (1 to 60 mM). Initially, there were no significant differences in the glucuronide rate of formation (pmol/min/mg protein) or total capacity (nmol/min/liver) between females and males. At the peak of maturation, the maximum rate of glucuronide formation was 4-fold less in females; however, the total capacity was 2-fold less in females due to the increased liver size in the females. The alterations in biotransformation coincided with increases in the hepatic and gonadal somatic indices and with changes in plasma hormone concentrations. These experiments provide insight into the metabolic deactivation of xenobiotics and to provide data for the prediction of altered hepatic biotransformation rates and pathways during the reproductive cycle.

Salicylic acid inhibition on browning of fresh-cut taro by regulating phenolic compounds and active oxygen metabolism

Surface browning of fresh-cut taro limits storage shelf-life and affects customer satisfaction. This study investigated the effects of salicylic acid (SA) on the browning of fresh-cut taro and explored the possible mechanism of SA in inhibiting browning. A 10 mmol/L SA treatment effectively delayed browning, improved soluble starch content, and reduced weight loss. Furthermore, by regulating the activities of phenylalanine ammonia-lyase (PAL) and polyphenol oxidase (PPO), SA treatment reduced the contents of total phenol, flavonoid, soluble quinone, and monomer phenolic acid, indicating that it inhibited phenol metabolism, decreased the synthesis of colored secondary metabolites, and suppressed surface browning in fresh-cut taro. On the other hand, SA treatment enhanced the activities of peroxidase (POD), catalase (CAT), and superoxide dismutase (SOD), reduced lipoxygenase (LOX) activity, enhanced ascorbic acid (AsA) and glutathione (GSH) levels. It decreased malondialdehyde (MDA), hydrogen peroxide (H2O2), and superoxide anion radicals (O2−·) production, indicating reduced oxidative damage. Thus, SA treatment improved the antioxidant system, reduced the accumulation of reactive oxygen species, and delayed phenolic oxidation, effectively inhibiting browning. These findings reveal SA as a feasible method for preserving fresh-cut fruits and vegetables.

Feasibility of intimately coupled CaO-catalytic-ozonation and bio-contact oxidation reactor for heavy metal and color removal and deep mineralization of refractory organics in actual coking wastewater

Considering the challenges for both single and traditional two-stage treatments, advanced oxidation and biodegradation, in the treatment of actual coking wastewater, an intimately coupled catalytic ozonation and biodegradation (ICOB) reactor was developed. In this study, ICOB treatment significantly enhanced the removal of Cu2+, Fe3+, and color by 39 %, 45 %, and 52 %, respectively, outperforming biodegradation. Catalytic ozonation effectively breaking down unsaturated organic substances and high-molecular-weight dissolved organic matter into smaller, more biodegradable molecules. Compared with biodegradation, the ICOB system significantly increased the abundances of Pseudomonas, Sphingopyxis, and Brevundimonas by ∼ 96 %, ∼67 %, and ∼ 85 %, respectively. These microorganisms, possessing genes for degrading phenol, aromatic compounds, polycyclic aromatics, and sulfur metabolism, further enhanced the mineralization of intermediates. Consequently, the ICOB system outperformed biodegradation and catalytic ozonation treatments, exhibiting chemical oxygen demand removal rate of ∼ 58 % and toxicity reduction of ∼ 47 %. Overall, the ICOB treatment showcases promise for practical engineering applications in coking wastewater treatment.

A Comparative Study of Phase I and II Hepatic Microsomal Biotransformation of Phenol in Three Species of Salmonidae: Hydroquinone, Catechol, and Phenylglucuronide Formation.

The in vitro biotransformation of phenol at 11 °C was studied using pre-spawn adult rainbow (Oncorhynchus mykiss) (RBT), brook (Salvelinus fontinalis) (BKT), and lake trout (Salvelinus namaycush) (LKT) hepatic microsomal preparations. The incubations were optimized for time, cofactor concentration, pH, and microsomal protein concentration. Formation of Phase I ring-hydroxylation and Phase II glucuronidation metabolites was quantified using HPLC with dual-channel electrochemical and UV detection. The biotransformation of phenol over a range of substrate concentrations (1 to 180 mM) was quantified, and the Michaelis-Menten kinetics constants, Km and Vmax, for the formation of hydroquinone (HQ), catechol (CAT), and phenylglucuronide (PG) were calculated. Species differences were noted in the Km values for Phase I enzyme production of HQ and CAT, with the following rank order of apparent enzyme affinity for substrate: RBT > BKT = LKT. However, no apparent differences in the Km for Phase II metabolism of phenol to PG were detected. Conversely, while there were no apparent differences in Vmax between species for HQ or CAT formation, the apparent maximum capacity for PG formation was significantly less in LKT than that observed for RBT and BKT. These experiments provide a means to quantify metabolic activation and deactivation of xenobiotics in fish, to compare activation and deactivation reactions across species, and to act as a guide for future predictions of new chemical biotransformation pathways and rates in fish. These experiments provided the necessary rate and capacity (Km and Vmax) inputs that are required to parameterize a fish physiologically based toxicokinetic (PB-TK) model for a reactive chemical that is readily biotransformed, such as phenol. In the future, an extensive database of these rate and capacity parameters on important fish species for selected chemical structures will be needed to allow the effective use of predictive models for reactive, biotransformation chemicals in aquatic toxicology and environmental risk assessment.