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PubMed2026

Genomic and Molecular Interaction Analysis of NodD1 in a Novel Bradyrhizobium yuanmingense sp. B64 Isolate for Nodulation and Symbiosis of Legume Plants.

Rhizobial bacteria are known for their ability to fix nitrogen for leguminous plants and their essential function for sustainable agriculture. This study characterizes the taxonomic status and functional potential of the Bradyrhizobium B64 isolate using integrated genomic and molecular approaches. The whole genome of the B64 isolate was sequenced via Illumina paired-end technology. Species delimitation was performed using average nucleotide identity (ANI) and digital DNA-DNA Hybridization (dDDH). The NodD1 protein structure was modeled using AlphaFold3 and validated by Ramachandran plot analysis. Molecular docking was then conducted to evaluate interactions between NodD1 and four signaling flavonoids: Apigenin, Daidzein, Genistein, and Naringenin. Genomic analysis revealed a maximum ANI of 94.4% and dDDH values between 51.4 and 62.4%. Since these values fall below the standard prokaryotic thresholds (ANI < 95%; dDDH < 70%), the B64 isolate is identified as a novel species. Physiological assays confirmed nitrogen fixation (1.97 ppm), IAA production (3.67 ppm), and phosphate solubilization (26.10 ppm). Structural validation showed 100% of NodD1 residues in allowed regions, ensuring high model reliability. Docking simulations demonstrated strong binding affinities across all flavonoids, with binding free energies ranging from - 8.8 to - 9.0 kcal/mol. Daidzein exhibited the highest thermodynamic stability (- 9.0 kcal/mol), whereas apigenin showed the most extensive residue interaction network. The B64 isolate is a novel Bradyrhizobium species with a high symbiotic capacity. The stable NodD1-flavonoid interactions provide a molecular basis for efficient nodulation, positioning B64 as a promising candidate for developing lipo-chitooligosaccharide (LCO)-based biofertilizers.

Bradyrhizobium↗

PubMed1986

The role of chalcone synthase in the regulation of flavonoid biosynthesis in developing oat primary leaves.

The role of chalcone synthase in the regulation of flavonoid biosynthesis during organogenesis of oat primary leaves has been investigated at the level of enzyme activity and mRNA translation in vitro. Chalcone synthase was purified about 500-fold. The apparent Km values were 1.5 and 6.3 microM for 4-coumaroyl-CoA and malonyl-CoA, respectively. The end products of oat flavonoid biosynthesis, three C-glucosylflavones, did not inhibit the reaction at concentrations as measured up to 60 microM each. Apigenin (4',5,7-trihydroxyflavone), a stable structural analog of the reaction product, 2',4,4',6'-tetrahydroxychalcone, was found to be a strong competitive inhibitor of 4-coumaroyl-CoA binding and a strong noncompetitive inhibitor of malonyl-CoA binding. Although apigenin is not supposed to be an intermediate of C-glucosylflavone biosynthesis, this compound might be a valuable tool for future kinetic studies. To date, there is no indication of chalcone synthase regulation by feedback or similar mechanisms which modulate enzyme activity. Mathematical correlation of chalcone synthase activity and flavonoid accumulation during leaf development, however, indicates that chalcone synthase is the rate-limiting enzyme of the pathway. By in vitro translation studies using preparations of total RNA from different leaf stages, we could demonstrate for the first time that the translational activity of chalcone synthase mRNA undergoes marked daily changes. The high values found at the end of the dark phase suggest that light does not exert direct influence on flavonoid biosynthesis but probably functions by controlling the basic diurnal rhythm.

Acyltransferases↗

PubMed1984

Flavonoid inhibition of human basophil histamine release stimulated by various agents.

Eleven naturally occurring flavonoids representing five different chemical classes were studied for their effects on human basophil histamine release triggered by six different stimuli. The flavonoids included flavone, quercetin, taxifolin, chalcone, apigenin, fisetin, rutin, phloretin, tangeretin, hesperetin, and naringin. The stimuli were antigen, anti-IgE, concanavalin A, ionophore A23187, formylmethionylleucylphenylalanine, and tetradecanoyl phorbol acetate. Concentration-effect relationships were established for each flavonoid (5-50 microM) at concentrations of stimuli which produced near optimal histamine release. Variable degrees of inhibition were noted depending on the nature of the stimulus and flavonoid structure. The flavonols, quercetin and fisetin, and the flavone, apigenin, exhibited a predilection to inhibit histamine release stimulated by IgE-dependent ligands (antigen, anti-IgE, and con A). The flavanone derivatives, taxifolin and hesperetin, were inactive, as were the glycosides, rutin and naringin. The open chain congeners, chalcone and phloretin, also possessed inhibitory activity. Thus, the flavonoids may be useful probes in comparative analysis of secretory phenomena. The findings suggest that the biochemical pathways leading to secretion differ subtly from one stimulus to another. The differences are detectable with flavonoids of different structures and possibly reflect distinct pathways of Ca2+ mobilization or other unique mechanisms of action.

Arachidonic Acid↗

PubMed1984

Modification of platelet function and arachidonic acid metabolism by bioflavonoids. Structure-activity relations.

The mechanism of the antiaggregating activity of flavonoids was studied in vitro. The activity of fifteen different compounds was tested on platelet aggregation and arachidonic acid metabolism. The effect of flavonoids on platelet adenosine 3',5'-cyclic monophosphate (cyclic AMP) levels under basal conditions, as well as after stimulation by prostacyclin (PGI2), was also measured. The glycons of flavonoids in general and the flavanone derivatives that we tested did not affect platelet function. On the other hand, flavone, chrysin , apigenin and phloretin inhibited platelet aggregation by depressing the cyclooxygenase pathway. In addition, flavone, chrysin and apigenin reduced the platelet cyclic AMP response to PGI2. This effect was probably mediated by an inhibition of adenylate cyclase. Myricetin and quercetin, however, increased the PGI2-stimulated rise of platelet cyclic AMP. Both of these flavonoids inhibited primarily lipoxygenase activity. Modification of platelet cyclic AMP metabolism through inhibition of phosphodiesterase activity was found to be the probable mechanism of their antiaggregating effect.

Arachidonic Acid↗

PubMed1992

Effects of synthetic and naturally occurring flavonoids on metabolic activation of benzo[a]pyrene in hamster embryo cell cultures.

Biochanin A, an isoflavone, has previously been shown to inhibit the metabolic activation of the carcinogen benzo[a]pyrene (B[a]P) to metabolites that bind to DNA in hamster embryo cells and are mutagenic in Chinese hamster V79 cells. To determine the structural features required for this activity and to attempt to find more effective inhibitors, a series of synthetic and naturally occurring flavonids were tested for their ability to modulate B[a]P metabolism in hamster embryo cell cultures. The observed structure-activity relationships indicate that the structural features of flavonoids important for effective inhibition of B[a]P metabolism in hamster embryo cells are the presence of two hydroxyl, two methoxyl, or methyl and hydroxyl substituents at the 5- and 7-positions and a 2,3-double bond. Flavones are slightly better inhibitors of B[a]P metabolism than the corresponding isoflavones. A substituent at the 4'-position is not essential for inhibition of B bdP metabolism. The presence of a hydroxyl group at position 3 slightly enhances activity. Apigenin, acacetin and kaempferide are effective inhibitors of B[a]P-induced mutagenesis in a hamster embryo cell-mediated V79 cell mutation assay. However, apigenin is cytotoxic at the inhibitory dose, whereas acacetin and kaempferide are not. These results suggest that acacetin and kaempferide are promising candidates for in vivo testing as potential chemopreventive agents.

Animals↗

PubMed1993

Vasodilatory effects of flavonoids in rat aortic smooth muscle. Structure-activity relationships.

1. Flavonoids relaxed the contractions induced by noradrenaline, KCl or phorbol 12-myristate, 13-acetate in rat aortic strips, the order of potency being: flavonols (quercetin, kaempferol, pentamethylquercetin) > flavones(luteolin, apigenin) > flavanols((+)-catechin, (-)-epicatechin) which correlates with the reported order of potency to inhibit protein kinase C. 2. The relaxant effects of kaempferol and luteolin were slightly potentiated by isoprenaline and those of pentamethylquercetin, kaempferol and apigenin by sodium nitroprusside. 3. It is concluded that the main vasodilatory mechanism of flavonoids seems to be the inhibition of protein kinase C. Inhibition of cyclic nucleotide phosphodiesterases or decreased Ca2+ uptake may also contribute to their vasodilatory effects.

3',5'-Cyclic-AMP Phosphodiesterases↗

PubMed2005

Luteolin, a flavonoid, inhibits AP-1 activation by basophils.

Flavonoids including luteolin, apigenin, and fisetin are inhibitors of IL-4 synthesis and CD40 ligand expression by basophils. This study was done to search for compounds with greater inhibitory activity of IL-4 expression and to clarify the molecular mechanisms through which flavonoids inhibit their expression. Of the 37 flavonoids and related compounds examined, ayanin, luteolin, and apigenin were the strongest inhibitors of IL-4 production by purified basophils in response to anti-IgE antibody plus IL-3. Luteolin did not suppress Syk or Lyn phosphorylation in basophils, nor did suppress p54/46 SAPK/JNK, p38 MAPK, and p44/42 MAPK activation by a basophilic cell line, KU812 cells, stimulated with A23187 and PMA. However, luteolin did inhibit phosphorylation of c-Jun and DNA binding activity of AP-1 in nuclear lysates from stimulated KU812 cells. These results provide a fundamental structure of flavonoids for IL-4 inhibition and demonstrate a novel action of flavonoids that suppresses the activation of AP-1.

Basophils↗

PubMed2005

Oral flavonoids delay recovery from experimental autoimmune encephalomyelitis in SJL mice.

Flavonoids are food components that appear to have potential beneficial health effects. There is a range of in vitro studies supporting the anti-oxidant and anti-inflammatory properties of flavonoids. Previously, we demonstrated that in vitro flavonoids, including luteolin and apigenin, inhibit proliferation and IFN-gamma production by murine and human autoimmune T cells. In the present study, we examined the effects of oral flavonoids as well as of curcumin on autoimmune T cell reactivity in mice and on the course of experimental autoimmune encephalomyelitis (EAE), a model for multiple sclerosis. Continuous oral administration of flavonoids significantly affected antigen-specific proliferation and IFN-gamma production by lymph node-derived T cells following immunization with an EAE-inducing peptide. Both luteolin and apigenin suppress proliferative responses as they did in vitro, whereas IFN-gamma production on the other hand was enhanced. Other flavonoids exerted differential effects on proliferation and IFN-gamma production. The effects of flavonoids and curcumin on EAE were assessed using either passive transfer of autoimmune T cells or active disease induction. In passive EAE, flavonoids led to delayed recovery of clinical symptoms rather than to any reduction in disease. In active EAE, the effects were less pronounced but also, in this case, the flavonoid hesperitin delayed recovery. Oral curcumin had overall mild but beneficial effects. Our results indicate that oral flavonoids fail to beneficially influence the course of EAE in mice but, instead, suppress recovery from acute inflammatory damage.

Administration, Oral↗

PubMed2006

Apiaceous vegetable constituents inhibit human cytochrome P-450 1A2 (hCYP1A2) activity and hCYP1A2-mediated mutagenicity of aflatoxin B1.

In humans, apiaceous vegetables (carrots, parsnips, celery, parsley, etc.) inhibit cytochrome P-450 1A2, a biotransformation enzyme known to activate several procarcinogens, including aflatoxin B1 (AFB). We evaluated eight phytochemicals from apiaceous vegetables for effects on human cytochrome P-450 1A2 (hCYP1A2) activity using a methoxyresorufin O-demethylase (MROD) assay and a trp-recombination assay. Saccharomyces cerevisiae was used for heterologous CYP1A2 expression and this yeast strain is also diploid and auxotrophic for tryptophan due to mutations in the trp5 alleles. When these two alleles undergo AFB-induced mitotic recombination, gene conversion occurs, allowing yeast to grow in the absence of tryptophan. The apiaceous constituents psoralen, 5-methoxypsoralen (5-MOP), 8-methoxypsoralen (8-MOP), and apigenin were potent inhibitors of hCYP1A2-mediated MROD activity in yeast microsomes, whereas quercetin was a modest hCYP1A2 inhibitor. Naringenin, caffeic acid, and chlorogenic acid did not inhibit hCYP1A2-mediated MROD activity. The 2-h pretreatment of intact yeast cells with psoralen, 5-MOP, and 8-MOP significantly improved cell survival after subsequent 4-h AFB treatment and reduced hCYP1A2-mediated mutagenicity of AFB. Apigenin also significantly decreased mutagenicity. These results suggest that in vivo CYP1A2 inhibition by apiaceous vegetables may be due to the phytochemicals present and imply that apiaceous vegetable intake may be chemopreventive by inhibiting CYP1A2-mediated carcinogen activation.

Aflatoxin B1↗

PubMed2004

Analysis of minor components in olive oil.

Virgin olive oil is well known for its high content of phenolic substances that are thought to have health-promoting properties. These substances also contribute to the distinctive taste of the oil. In this study, tyrosol, vanillic acid, luteolin, and apigenin were identified and quantified by liquid chromatography mass spectrometry (LC-MS). In the seven samples analysed, tyrosol, the most abundant, was in the range of 1.4-29 mg/kg, vanillic acid was in the range of 0.67-4.0 mg/kg, luteolin was in the range of 0.22-7.0 mg/kg, and apigenin was in the range of 0.68-1.6 mg/kg. It was also shown that in olive oil, squalene can be analysed by using a refractive index detector. In the samples analysed, squalene occurred in the range of 3.9-9.6 g/l.

Chromatography, Liquid↗

PubMed2005

Regiospecific methylation of naringenin to ponciretin by soybean O-methyltransferase expressed in Escherichia coli.

Flavonoids found in plants most likely undergo a variety of modification reactions such as hydroxylation, glycosylation, and/or methylation. Among these, O-methylation has an effect on the solubility and thus on the antimicrobial activity of the flavonoids. We analyzed the conversion of naringenin with a methyltransferase, SOMT-2, from Glycine max. SOMT-2 was expressed in Escherichia coli as a glutathion S-transferase fusion protein. E. coli harboring SOMT-2 was grown with daidzein, geninstein, apigenin, naringenin, and quercetin, respectively, and reaction products were analyzed with thin layer chromatography and HPLC. SOMT-2 could convert apigenin, daidzein, genistein, and quercetin into the corresponding 4'-O-methylated compounds such as acacetin, formononetin, biochanine A, and 4'-methylated quercetin whereas naringenin turned out to be the best substrate tested. SOMT-2 stoichiometically converted naringenin (4',5,7-trihyroxyflavanone) into a ponciretin (4'-methoxy-5,7-dihydroxyflavanone), whose structure was determined by NMR and LC/mass spectral analyses. Considering the reactions, SOMT-2 may have a regiospecific methylation activity, resulting in transforming 4'-hydroxyl group of flavonoids B-ring to 4'-methyl group.

Biotransformation↗

PubMed2006

Regioselectivity of 7-O-methyltransferase of poplar to flavones.

POMT-7, an O-methyltransferase from poplar (Populus deltoids) was used to modify a variety of flavonoid compounds. POMT-7 was able to transfer a methyl group to several flavonoids containing a C-7 hydroxyl group. However, POMT-7 showed a higher affinity toward flavonol and flavone such as apigenin, kaempferol, luteolin, and quercetin than flavanone and isoflavone. Based on comparison of HPLC retention times with authentic compounds and corresponding nuclear magnetic resonance spectroscopy data, the methylation position of the reaction products was determined to be at the hydroxyl group of C-7. Biotransformation kinetics indicated that the enzyme converted more than 80% of the apigenin, kaempferol, luteolin and quercetin substrates, which were added at concentration of 70 microM, into corresponding 7-methoxy compounds within 24 h.

Flavones↗

PubMed2006

Cytotoxicity and in vitro susceptibility of Entamoeba histolytica to Morinda morindoides leaf extracts and its isolated constituents.

An aqueous decotion (dried extract), an 80% MeOH extract from Morinda morindoides leaves, and 10 flavonoids and 4 iridoids isolated from the 80% MeOH extract were evaluated in vitro for their potential antiamoebic activity and their cytotoxic effect against MT-4 cells. Results indicated that the aqueous decoction and the 80% MeOH extract exhibited an interesting antiamoebic activity with IC(50) values of 3.1 +/- 1.7 and 1.7 +/- 0.6 microg/ml, respectively. Apigenin-7-O-glucoside and luteolin-7-O-glucoside exhibited a moderate antiamoebic activity with IC(50) values of 22.3 +/- 3.2 and 37.4 +/- 2.7 microg/ml, respectively. Kaempferol (IC(50) = 10.3 +/- 2.3 microg/ml), apigenin (IC(50) = 12.7 +/- 4.3 microg/ml), and luteolin (IC(50) = 17.8 +/- 4.3 microg/ml) showed a more pronounced activity than their corresponding glycosides. All tested iridoids displayed a very good activity with IC(50) values less than 10 microg/ml. The most active iridoids were epoxygaertneroside (IC(50) = 1.3 +/- 0.4 microg/ml) and methoxygaertneroside (IC(50) = 2.3. +/- 0.7), followed by gaertneroside and gaertneric acid with IC(50) values of 4.3 +/- 1.8 and 7.1 +/- 1.4 microg/ml, respectively. Except quercetin and quercetin-7,4'-dimethylether which have shown a cytotoxic effect with IC(50) ranging from 14 to 22 microg/ml. No correlation could be deduced between the observed antiamoebic and cytotoxic activity of these tested samples. A structure-activity relationship for isolated compounds is discussed. These findings support the medicinal report for the traditional use of Morinda morindoides leaves for the treatment of amoebiasis.

Amebicides↗

PubMed2006

Quantitative determination of apogossypol, a pro-apoptotic analog of gossypol, in mouse plasma using LC/MS/MS.

A simple and selective liquid chromatography/tandem mass spectrometry (LC/MS/MS) method based on internal standard quantitation using apigenin as the internal standard has been developed and validated for the analysis of the gossypol analog apogossypol, a pro-apoptotic compound, in mouse plasma. The methodology involves protein precipitation of plasma samples followed by LC/MS/MS analysis. Ascorbic acid was added to the spiking solutions and plasma samples to stabilize the easily oxidized compound. Separation of apogossypol and the internal standard from the plasma matrix was achieved using a C18 column with a gradient elution profile consisting of 5mM ammonium acetate and methanol. The validated range of the method extended from 10 to 2000 ng/mL with accuracies of 85-115% and precision of <15%. The average recovery of apogossypol at three concentrations (50, 200 and 1000 ng/mL) assayed in triplicate using this methodology was determined to be 90.8+/-12.9%. Recovery for the internal standard (apigenin) at a concentration of 500 ng/mL was found to be 99.9+/-6.41%. Apogossypol concentrations of 50 ng/mL and above were found to be stable in extracted plasma for 24h when stored at 25 degrees C. This method has been applied to the determination of apogossypol concentrations in plasma collected from mice given an IV dose of apogossypol.

Animals↗

PubMed2005

Dose-response effects of phytoestrogens on the activity and expression of 3beta-hydroxysteroid dehydrogenase and aromatase in human granulosa-luteal cells.

There is evidence that certain phytoestrogens can inhibit key steroidogenic enzymes although most studies have been carried out on microsomal or purified enzyme preparations, some using cell lines. This study was designed to test the hypothesis that low doses of phytoestrogens, at concentrations that would be attained through the diet, could inhibit 3beta-hydroxysteroid dehydrogenase (HSD) and/or aromatase in primary cultures of human granulosa-luteal (GL) cells and that this effect was due to a decrease in the expression of these proteins. Based on published evidence, eight compounds were selected for investigation and these included the flavones apigenin and quercetin, the isoflavones genistein, biochanin A and daidzein, the lignans, enterodiol and enterolactone, and the mycotoxin zearalenone. Human GL cells were cultured for 48 h in the presence of these phytoestrogens at concentrations ranging from 0.01 to 100 microM and after addition of fresh media the conversion of pregnenolone to progesterone or androstenedione to oestradiol over a 4h period was measured. Biochanin A was the only phytoestrogen that displayed any dose-dependent inhibition of 3beta-HSD, others showing inhibition at doses >/=10 microM. Apigenin and quercetin only inhibited aromatase/17beta-HSD at high doses as did genistein, biochanin A and daidzein. The lignans had weak inhibitory effects on aromatase/17beta-HSD, whilst zearalenone showed potent inhibition at 0.1 microM. Phytoestrogens did not exert any significant effects on protein expression of 3beta-HSD or aromatase as determined by Western blots. It is concluded that steroidogenic enzymes are inhibited by phytoestrogens in primary cultures of human GL cells but these cells are less sensitive to the effects of phytoestrogens than cell-free systems. This may be due to poor lipid solubility or cellular metabolism. We have also shown for the first time that phytoestrogens do not act by inhibiting the cellular concentration of 3beta-HSD and aromatase even though exposure time would have allowed for changes in gene expression.

3-Hydroxysteroid Dehydrogenases↗

PubMed2006

Phytoestrogens and their low dose combinations inhibit mRNA expression and activity of aromatase in human granulosa-luteal cells.

There is evidence that certain phytoestrogens inhibit aromatase, the enzyme that converts androgens to oestrogens. Kinetic studies in cell-free preparations show that they may inhibit aromatase by competitive binding to the enzyme, but there is a paucity of studies investigating longer-term effects of phytoestrogens on the expression of steroidogenic enzymes. This study tested the hypothesis that phytoestrogens could reduce aromatase activity by down-regulation of its expression. Experiments were carried out on primary cultures of human granulosa-luteal (GL) cells after they had been exposed to phytoestrogens for 48 h. Aromatase activity was measured by the ability of cells to convert testosterone to estradiol over a 4h period and aromatase mRNA expression (mRNA(arom)) was subsequently measured from the same cells using quantitative real-time PCR. The compounds investigated were the flavones, apigenin and quercetin, and the isoflavones, genistein, biochanin A and daidzein at doses of 10 microM and 100 nM. Combinations of these compounds at the lower dose were also investigated. All compounds tested dose-dependently reduced mean mRNA(arom) compared with controls. Apigenin was the most potent inhibitor with significant inhibition of mRNA(arom) seen at both 10 microM and 100 nM, whilst other flavonoids (except biochanin A) only induced significant inhibition (p<or=0.05) at the higher dose. Low dose (100 nM) mixtures of the compounds were ineffective except for a combination of the three isoflavones that induced a significant inhibition of mRNA(arom). The changes in aromatase activity paralleled the mRNA(arom) results and additional studies showed that the reduction in aromatase activity was significantly delayed in time compared with the reduction in mRNA(arom.) This is the first study to compare the action of various phytoestrogens, either singly or in low-dose combination, on the expression and activity of aromatase in human cells and it suggests that chronic dietary exposure and tissue accumulation of low-dose mixtures of phytoestrogens could have important consequences for aromatase activity and the production of oestrogens.

Aromatase↗

PubMed2006

Aromatic diglycosides from Cladogynos orientalis.

Two unusual aromatic diglycosides with galloyl substitution, 4''-O-galloyl-violutoside and 4''-O-galloyl-benzyl-O-alpha-L-rhamnopyranosyl-(1-->6)-beta-D-glucopyranoside, were isolated from the aerial portion of Cladogynos orientalis along with isovitexin, apigenin 6-C-(2''-O-galloyl)-beta-D-glucopyranoside, apigenin 8-C-(2''-O-galloyl)-beta-D-glucopyranoside, syringic acid beta-D-glucopyranoside, 3,4,5-trimethoxyphenyl beta-D-glucopyranoside, (6S,9R)-roseoside, and violutioside. The structural elucidations were based on analyses of chemical and spectroscopic data by including 1D and 2D NMR analyses.

Euphorbiaceae↗

PubMed2001

Effects of structurally related flavonoids on cell cycle progression of human melanoma cells: regulation of cyclin-dependent kinases CDK2 and CDK1.

We have investigated the effects of a series of flavonoids on cell proliferation and cell cycle distribution in human melanoma cells OCM-1. Among the compounds that potently inhibited OCM-1 cell proliferation, we show that the presence of a hydroxyl group at the 3'-position of the ring B in quercetin and luteolin, correlated to a G1 cell cycle arrest while its absence in kaempferol and apigenin correlated to a G2 block. Genistein with a hydroxyl at 5-position of the ring A arrested cells in G2 while daidzein which lacks it, induced an accumulation of cells in G1. We demonstrate that flavonoids, which induced a cell cycle block in G1, inhibited the activity of CDK2 by 40-60%. By contrast, those which caused an accumulation of cells in G2/M were without effect. On the other hand, while quercetin, daidzein and luteolin did not alter the activity of CDK1, kaempferol, apigenin and genistein inhibited this kinase by 50-70%. We demonstrate that the up-regulation of the CDK inhibitors p27(KIP1) and p21(CIP1) is likely responsible for the inhibition of CDK2 while inhibition of CDK1 was rather due to the phosphorylation of the kinase on Tyr15 residue.

CDC2 Protein Kinase↗