Effects of cobalt-substitution of the active zinc ion in thermolysin on its activity and active-site microenvironment

Thermolysin is remarkably activated in the presence of high concentrations (1-5 M) of neutral salts [Inouye, K. (1992) J. Biochem. 112, 335-340]. The activity is enhanced 13-15 times with 4 M NaCl at pH 7.0 and 25 degrees C. Substitution of the active site zinc with other transition metals alters the activity of thermolysin [Holmquist, B. and Vallee, B.L. (1974) J. Biol. Chem. 249, 4601-4607]. Cobalt is the most effective among the transition metals and doubles the activity toward N-[3-(2-furyl)acryloyl]-glycyl-L-leucine amide. In this study, the effect of NaCl on the activity of cobalt-substituted thermolysin was examined. Cobalt-substituted thermolysin, with 2.8-fold increased activity compared with the native enzyme, is further activated by the addition of NaCl in an exponential fashion, and the activity is enhanced 13-15 times at 4 M NaCl. The effects of cobalt-substitution and the addition of salt are independent of each other. The activity of cobalt-substituted thermolysin, expressed as k(cat)/K(m), is pH-dependent and controlled by at least two ionizing residues with pK(a) values of 6.0 and 7.8, the acidic pK(a) being slightly higher compared to 5.6 of the native enzyme. These pK(a) values remain constant in the presence of 4 M NaCl, indicating that the electrostatic environment of cobalt-substituted thermolysin is more stable than that of the native enzyme, the acidic pK(a) of which shifts remarkably from 5.6 to 6.7 at 4 M NaCl. Zincov, a competitive inhibitor, binds more tightly to the cobalt-substituted than to native thermolysin at pH 4.9-9.0, probably because of its preference for cobalt in the fivefold coordination. The cobalt substitution has been shown to be a favorable tool with which to explore the active-site microenvironment of thermolysin.

Structure-function analysis of CYP27B1 and CYP27A1. Studies on mutants from patients with vitamin D-dependent rickets type I (VDDR-I) and cerebrotendinous xanthomatosis (CTX)

We have determined eight types of missense mutants of CYP27B1 from Japanese vitamin D-dependent rickets type I (VDDR-I) patients [Kitanaka, S., Takeyama, K., Murayama, A., Sato, T., Okumura, K., Nogami, M., Hasegawa, Y., Niimi, H., Yanagisawa, J., Tanaka, T. & Kato, S. (1998) New England J. Med., 338, 653-661 and Kitanaka, S., Murayama, A., Sakaki, T., Inouye, K., Seino, Y., Fukumoto, S., Shima, M., Yukizane, S., Takayanagi, M., Niimi, H., Takeyama, K. & Kato, S. (1999) J. Clin. Endocrine Metab., 84, 4111-4117]. None of the CYP27B1 mutants showed 1alpha-hydroxylase activity towards 25-hydroxyvitamin D3. Thus, it was assumed that the mutated amino-acid residues play important roles in the 1alpha-hydroxylase activity, such as substrate binding, activation of molecular oxygen, interaction with adrenodoxin, and folding of the cytochrome P450 structure. To examine our hypothesis, we generated various mutants of CYP27B1 and studied their enzymatic properties. In addition, the corresponding mutations were introduced to CYP27A1, which belongs to the same family as CYP27B1. As CYP27A1 showed much higher expression level than CYP27B1 in Escherichia coli, further analysis including heme-binding and substrate-binding was performed with CYP27A1 in place of CYP27B1. Western blot analysis, spectral analysis including reduced CO-difference spectra and substrate-induced difference spectra, and enzymatic analysis of the mutant CYP27A1 gave information on the structure-function relationships of both CYP27A1 and CYP27B1. Although the sequence alignment suggested that Arg107, Gly125, and Pro497 of CYP27B1 might be involved in substrate binding, the experimental data strongly suggested that mutations of these amino-acid residues destroyed the tertiary structure of the substrate-heme pocket. It was also suggested that Arg389 and Arg453 of CYP27B1 were involved in heme-propionate binding, and Asp164 stabilized the four-helix bundle consisting of D, E, I and J helices, possibly by forming a salt bridge. Thr321 was found to be responsible for the activation of molecular oxygen.

Involvement of B-Raf in Ras-induced Raf-1 activation

The mechanism of Ras-induced Raf-1 activation is not fully understood. Previously, we identified a 400-kDa protein complex as a Ras-dependent Raf-1 activator. In this study, we identified B-Raf as a component of this complex. B-Raf was concentrated during the purification of the activator. Immunodepletion of B-Raf abolished the effect of the activator on Raf-1. Furthermore, B-Raf and Ras-activated Raf-1 co-operatively, when co-transfected into human embryonic kidney 293 cells. On the other hand, Ras-dependent extracellular signal-regulated kinase/mitogen-activated protein kinase kinase stimulator (a complex of B-Raf and 14-3-3) failed to activate Raf-1 in our cell-free system. These results suggest that B-Raf is an essential component of the Ras-dependent Raf-1 activator.

Molecular regulation of the hypothalamo-pituitary-adrenal axis in streptozotocin-induced diabetes: effects of insulin treatment

Increased hypothalamo-pituitary-adrenocortical (HPA) activity in diabetes is likely important in the development of some pathologies associated with the disorder. We hypothesized that central regulation of HPA activity differs among normal, streptozotocin (STZ)-diabetic, and insulin-treated diabetic rats. Blood glucose, ACTH, and corticosterone were elevated, 8 d after inducing diabetes. Insulin treatment normalized these parameters. Plasma norepinephrine was similar in all groups, but epinephrine was lower in STZ-diabetic and higher in insulin-treated rats vs. normals. Increased ACTH with diabetes corresponded with increased hypothalamic CRH mRNA, but no change in pituitary POMC mRNA. With insulin-treatment, CRH mRNA remained elevated, and POMC mRNA was unaltered. Hippocampal MR mRNA expression was dramatically increased with diabetes and, moreover, was not normalized by insulin. No differences in GR mRNA were detected between normal and STZ-diabetic rats. However, insulin treatment increased GR mRNA levels in the paraventricular nucleus and pituitary. We postulate that, in STZ-diabetes: 1) increased HPA activity is caused by increased central drive at and/or above the level of the paraventricular nucleus and is associated with decreased epinephrine; and 2) normalized pituitary-adrenal activity with insulin may be caused by the compensatory increase in GR mRNA allowing glucocorticoid-mediated suppression of ACTH secretion despite the residual increase in central HPA activity. Thus, insulin apparently restored HPA activity at and below the pituitary but, surprisingly, not above it.

Effects of antecedent hypoglycemia, hyperinsulinemia, and excess corticosterone on hypoglycemic counterregulation

This study aimed to differentiate the effects of repeated antecedent hypoglycemia, antecedent marked hyperinsulinemia, and antecedent increases in corticosterone on counterregulation to subsequent hypoglycemia in normal rats. Specifically, we examined whether exposure to hyperinsulinemia or elevated corticosterone per se could impair subsequent counterregulation. Four groups of male Sprague-Dawley rats were used: 1) normal controls (N) had 4 days of sham antecedent treatment; 2) an antecedent hypoglycemia group (AH) had 7 episodes of hyperinsulinemic hypoglycemia over 4 days; 3) an antecedent hyperinsulinemia group (AE) had 7 episodes of hyperinsulinemic euglycemia; and 4) an antecedent corticosterone group (AC) had 7 episodes of intravenous corticosterone to simulate the hypoglycemic corticosterone levels in AH rats. On day 5, hyperinsulinemic euglycemic-hypoglycemic clamps were performed. Epinephrine responses to hypoglycemia were impaired (P < 0.05 vs. N) after antecedent hypoglycemia and hyperinsulinemia. This correlated with diminished (P < 0.05 vs. N) absolute glucose production responses in AH rats and diminished incremental glucose production responses in AE rats. Paradoxically, norepinephrine responses were increased (P < 0.05 vs. N) after antecedent hypoglycemia. Glucagon and corticosterone responses were unaffected by antecedent hypoglycemia and hyperinsulinemia. In AC rats, incremental but not absolute glucose production responses were decreased (P < 0.05 vs. N). However, neuroendocrine counterregulation was unaltered. We conclude that both antecedent hypoglycemia and hyperinsulinemia impair epinephrine and glucose production responses to subsequent hypoglycemia, suggesting that severe recurrent hyperinsulinemia may contribute to the development of hypoglycemia-associated autonomic failure.

Myosin II-dependent cylindrical protrusions induced by quinine inDictyostelium: antagonizing effects of actin polymerization at the leading edge

We found that amoeboid cells of Dictyostelium are induced by a millimolar concentration of quinine to form a rapidly elongating, cylindrical protrusion, which often led to sustained locomotion of the cells. Formation of the protrusion was initiated by fusion of a contractile vacuole with the cell membrane. During protrusion extension, a patch of the contractile vacuole membrane stayed undiffused on the leading edge of the protrusion for over 30 seconds. Protrusion formation was not inhibited by high osmolarity of the external medium (at least up to 400 mosM). By contrast, mutant cells lacking myosin II (mhc− cells) failed to extend protrusions upon exposure to quinine. When GFP-myosin-expressing cells were exposed to quinine, GFP-myosin was accumulated in the cell periphery forming a layer under the cell membrane, but a newly formed protrusion was initially devoid of a GFP-myosin layer, which gradually formed and extended from the base of the protrusion. F-actin was absent in the leading front of the protrusion during the period of its rapid elongation, and the formation of a layer of F-actin in the front was closely correlated with its slowing-down or retraction. Periodical or continuous detachment of the F-actin layer from the apical membrane of the protrusion, accompanied by a transient increase in the elongation speed at the site of detachment, was observed in some of the protrusions. The detached F-actin layers, which formed a spiral layer of F-actin in the case of continuous detachment, moved in the opposite direction of protrusion elongation. In the presence of both cytochalasin A and quinine, the protrusions formed were not cylindrical but spherical, which swallowed up the entire cellular contents. The estimated bulk flux into the expanding spherical protrusions of such cells was four-times higher than the flux into the elongating cylindrical protrusions of the cells treated with quinine alone. These results indicate that the force responsible for the quinine-induced protrusion is mainly due to contraction of the cell body, which requires normal myosin II functions, while actin polymerization is important in restricting the direction of its expansion. We will discuss the possible significance of tail contraction in cell movement in the multicellular phase of Dictyostelium development, where cell locomotion similar to that induced by quinine is often observed without quinine treatment, and in protrusion elongation in general.

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Pepsin digestion of a mouse monoclonal antibody of IgG1 class formed F(ab')(2) fragments in which the light chains as well as the heavy chains were truncated

In the preparation of F(ab')(2) fragments of monoclonal antibodies (mAbs) of IgG class, heavy (H) chains are truncated by pepsin and light (L) chains are remained intact. However, F(ab')(2) fragments formed by pepsin-digestion of a mouse mAb PM373, which was of the IgG1 class and raised against human prostate specific antigen (PSA), indicated that the L chains of 31 kDa were cleaved into 23-kDa fragments as well as the cleavage of H chains of 50 kDa into 28-kDa fragments. On the other hand, F(ab')(2) fragments formed by digesting the mAb by cathepsin D showed that the L chains were intact and the H chains were truncated. The immunoreactivities against PSA of the F(ab')(2) fragments containing the intact L chains and those containing the truncated L chains were almost the same as that of the parental mAb, suggesting that the truncation of the L chains does not affect the interaction of the mAb with its specific antigen.

Interactions of human matrix metalloproteinase 7 (matrilysin) with the inhibitors thiorphan and R-94138

The effects of the metalloproteinase inhibitors thiorphan and R-94138 on the matrilysin-catalyzed hydrolysis of (7-methoxycoumarin-4-yl)acetyl-L-Pro-L-Leu-Gly-L-Leu-[N(3)-(2,4-dinitrophenyl)-L-2,3-diamino-propionyl]-L-Ala-L-Arg-NH(2) [MOCAc-PLGL(Dpa)AR] were examined. The inhibitor constants (K(i)) of thiorphan and R-94138 for matrilysin at pH 7.5, 25 degrees C were determined to be 11.2 and 7.65 microM, respectively. From the temperature dependence of the K(i) values at pH 7.5, the standard enthalpy change (Delta H degrees ') values for the binding of matrilysin with thiorphan and R-94138 were determined to be -(18.2 +/- 0.9) and (1.65 +/- 1.07) kJ x mol(-1), respectively. The binding of matrilysin to thiorphan is exothermic and the free energy change in the complex formation depends mainly on the change in enthalpy, while the binding to R-94138 is endothermic and typically entropy-driven. Hydrophobic interactions are suggested to contribute significantly to the binding of matrilysin to R-94138 as well as to the substrate. The pH dependence of the K(i) value suggests that at least two ionizing groups with pK(a) values of 4.5 and 9.1--9.3 are involved in the binding. The matrilysin activity is regulated by ionizing groups with pK(a) values of 4.3 and 9.6. Both inhibition and hydrolysis are suggested to be controlled by the same residues in matrilysin, most likely Glu 198 and Tyr 219, respectively.

Screening of the Bacillus thuringiensis Cry1Ac delta-endotoxin on the artificial phospholipid monolayer incorporated with brush border membrane vesicles of Plutella xylostella by optical biosensor technology

The binding of Cry1Ac, an insecticidal protein of Bacillus thuringiensis, to a brush border membrane (BBM) isolated from midguts of the diamondback moth Plutella xylostella was examined by surface plasmon resonance (SPR)-based biosensor. BBM was mixed with 1,3-ditetradecylglycero-2-phosphocholine (PC14), a neutral charged artificial lipid, and was reconstructed to a monolayer on a hydrophobic chip for the biosensor. The binding of Cry1Ac to the reconstructed monolayer was analyzed by a two-state binding model, and it was shown that Cry1Ac bound to the monolayer in the first step with an affinity constant (K(1)) of 508 nM, followed by the second uni-molecular step with an equilibrium constant (K(2)) of 0.472. The overall affinity constant K(d) was determined to be 240 nM. The binding was markedly inhibited by N-acetyl-D-galactosamine (K(i)=8 mM). The monolayer was shown to retain a high affinity to Cry1Ac, providing an insect-free system for rapid and large-scale screening of B. thuringiensis insecticidal proteins by the SPR-based biosensor technology.

Inhibitory effects of detergents on rat CYP1A1-dependent monooxygenase: comparison of mixed and fused systems consisting of rat CYP 1A1 and yeast NADPH-P450 reductase

Inhibitory effects of detergents Triton X-100 and Chaps on 7-ethoxycoumarin O-deethylation activity were examined in the recombinant microsomes containing both rat CYP1A1 and yeast NADPH-P450 reductase (the mixed system) and their fused enzyme (the fused system). Triton X-100 showed competitive inhibition in both mixed and fused systems with K(i) values of 24.6 and 21.5 microM, respectively. These results strongly suggest that Triton X-100 binds to the substrate-binding pocket of CYP1A1. These K(i) values are far below the critical micelle concentration of Triton X-100 (240 microM). Western blot analysis revealed no disruption of the microsomal membrane by Triton X-100 in the presence of 0-77 microM Triton X-100. On the other hand, Chaps gave distinct inhibitory effects to the mixed and fused systems. In the fused system, a mixed-type inhibition was observed with K(i) and K(i)' values of 1.2 and 5.4 mM of Chaps, respectively. However, in the mixed system, multiple inhibition modes by Chaps were observed. Western blot analysis revealed that the solubilized fused enzyme by Chaps preserved the activity whereas the solubilized CYP1A1 and NADPH-P450 reductase reductase showed no activity in the mixed system. Thus, the comparison of the mixed and fused systems appears quite useful to elucidate inhibition mechanism of detergents.

Effects of dimethyl sulfoxide, temperature, and sodium chloride on the activity of human matrix metalloproteinase 7 (matrilysin)

Effects of dimethyl sulfoxide (DMSO), temperature, and sodium chloride on the matrilysin-catalyzed hydrolysis of (7-methoxycoumarin-4-yl)acetyl-L-Pro-L-Leu-Gly-L-Leu-[N(3)-(2, 4-dinitrophenyl)-L-2,3-diamino-propionyl]-L-Ala-L-Arg-NH(2) [MOCAc-PLGL(Dpa)AR] were examined. DMSO inhibited the matrilysin activity competitively with the inhibitor constant (K(i)) of 0. 59+/-0.04 M, and the binding between them was endothermic and entropy-driven. The binding of matrilysin with MOCAc-PLGL(Dpa)AR was also found to be entropy-driven. The matrilysin activity was increased in a biphasic exponential fashion with increasing concentration of NaCl, and was 5.3 times higher in the presence of 4 M NaCl than that in its absence. The first and second phases were separated at 0.5 M NaCl, and the activation at x M NaCl compared with the activity in the absence of NaCl was expressed as 2.1(x) at [NaCl] < 0.5 M and 1.4(x) at [NaCl] > 0.5 M. The activation was brought about solely through a decrease in the Michaelis constant (K(m)), and the catalytic constant (k(cat)) was not much altered. This suggests that the decrease in the electrostatic interaction and the increase in the hydrophobic interaction between matrilysin and the substrate might enhance the enzyme activity by reducing the K(m) value.

Dual metabolic pathway of 25-hydroxyvitamin D3 catalyzed by human CYP24

Human 25-hydroxyvitamin D3 (25(OH)D3) 24-hydroxylase (CYP24) cDNA was expressed in Escherichia coli, and its enzymatic and spectral properties were revealed. The reconstituted system containing the membrane fraction prepared from recombinant E. coli cells, adrenodoxin and adrenodoxin reductase was examined for the metabolism of 25(OH)D3, 1alpha,25(OH)2D3 and their related compounds. Human CYP24 demonstrated a remarkable metabolism consisting of both C-23 and C-24 hydroxylation pathways towards both 25(OH)D3 and 1alpha,25(OH)2D3, whereas rat CYP24 showed almost no C-23 hydroxylation pathway [Sakaki, T. Sawada, N. Nonaka, Y. Ohyama, Y. & Inouye, K. (1999) Eur. J. Biochem. 262, 43-48]. HPLC analysis and mass spectrometric analysis revealed that human CYP24 catalyzed all the steps of the C-23 hydroxylation pathway from 25(OH)D3 via 23S, 25(OH)2D3, 23S,25,26(OH)3D3 and 25(OH)D3-26,23-lactol to 25(OH)D3-26, 23-lactone in addition to the C-24 hydroxylation pathway from 25(OH)D3 via 24R,25(OH)2D3, 24-oxo-25(OH)D3, 24-oxo-23S,25(OH)2D3 to 24,25,26,27-tetranor-23(OH)D3. On 1alpha,25(OH)2D3 metabolism, similar results were observed. These results strongly suggest that the single enzyme human CYP24 is greatly responsible for the metabolism of both 25(OH)D3 and 1alpha,25(OH)2D3. We also succeeded in the coexpression of CYP24, adrenodoxin and NADPH-adrenodoxin reductase in E. coli. Addition of 25(OH)D3 to the recombinant E. coli cell culture yielded most of the metabolites in both the C-23 and C-24 hydroxylation pathways. Thus, the E. coli expression system for human CYP24 appears quite useful in predicting the metabolism of vitamin D analogs used as drugs.

Biphasic kinetic behavior of rat cytochrome P-4501A1-dependent monooxygenation in recombinant yeast microsomes

Rat cytochrome P-4501A1-dependent monooxygenase activities were examined in detail using recombinant yeast microsomes containing rat cytochrome P-4501A1 and yeast NADPH-P-450 reductase. On 7-ethoxycoumarin, which is one of the most popular substrates of P-4501A1, the relationship between the initial velocity (v) and the substrate concentration ([S]) exhibited non-linear Michaelis-Menten kinetics. Hanes-Woolf plots ([S]/v vs. [S]) clearly showed a biphasic kinetic behavior. Aminopyrine N-demethylation also showed a biphasic kinetics. The regression analyses on the basis of the two-substrate binding model proposed by Korzekwa et al. (Biochemistry 37 (1998) 4137-4147) strongly suggest the presence of the two substrate-binding sites in P-4501A1 molecules for those substrates. An Arrhenius plot with high 7-ethoxycoumarin concentration showed a breakpoint at around 28 degrees C probably due to the change of the rate-limiting step of P-4501A1-dependent 7-ethoxycoumarin O-deethylation. However, the addition of 30% glycerol to the reaction mixture prevented observation of the breakpoint. The methanol used as a solvent of 7-ethoxycoumarin was found to be a non-competitive inhibitor. Based on the inhibition kinetics, the real V(max) value in the absence of methanol was calculated. These results strongly suggest that the recombinant yeast microsomal membrane containing a single P-450 isoform and yeast NADPH-P-450 reductase is quite useful for kinetic studies on P-450-dependent monooxygenation including an exact evaluation of inhibitory effects of organic solvents.

Coexpression of genetically engineered fused enzyme between yeast NADPH-P450 reductase and human cytochrome P450 3A4 and human cytochrome b5 in yeast

Human hepatic cytochrome P450 3A4 (CYP3A4) was expressed in yeast Saccharomyces cerevisiae. While the expression level was high as compared with other human hepatic cytochrome P450s, CYP3A4 showed almost no catalytic activity toward testosterone. Coexpression of CYP3A4 with yeast NADPH-P450 reductase did not give a full activity. Low monooxygenase activity of CYP3A4 was attributed to the insufficient reduction of heme iron of CYP3A4 by NADPH-P450 reductase. To enhance the efficiency of electron transfer from NADPH-P450 reductase to CYP3A4, a fused enzyme was constructed between CYP3A4 and yeast NADPH-P450 reductase. The rapid reduction of the heme iron of the fused enzyme by NADPH was observed. The fused enzyme showed a high testosterone 6beta-hydroxylation activity with a sigmoidal velocity saturation curve. However, the coupling efficiency between NADPH utilization and testosterone 6beta-hydroxylation was only 10%. Finally, coexpression of the fused enzyme and human cytochrome b5 was examined. A significant decrease in the Km value and a remarkable increase in the coupling efficiency were observed. Substrate-induced spectra revealed that the dissociation constant of the fused enzyme for testosterone significantly decreased with coexpression of human cytochrome b5. These results strongly suggest that human cytochrome b5 directly interacts with the CYP3A4 domain of the fused enzyme and modifies the tertiary structure of substrate binding pocket, resulting in tight binding of the substrate and high coupling efficiency.

States of tryptophyl residues and stability of recombinant human matrix metalloproteinase 7 (matrilysin) as examined by fluorescence

States of tryptophyl residues and stability of human matrilysin were studied. The activation energy for the thermal inactivation of matrilysin was determined to be 237 kJ/mol, and 50% of the activity was lost upon incubation at 69 degrees C for 10 min. The activity was increased by adding NaCl, and was doubled with 3 M NaCl. Denaturation of matrilysin by guanidine hydrochloride (GdnHCl) and urea was monitored by fluorescence change of tryptophyl residues. Half of the change was observed at 2.2-2.7 M GdnHCl, whereas no change was observed even with 8 M urea. Half of the inactivation was induced at 0.8 M GndHCl and at 2 M urea. The presence of an inactive intermediate with the same fluorescence spectrum as the native enzyme was suggested in the denaturation. Matrilysin contains four tryptophyls, and their states were examined by fluorescence-quenching with iodide and cesium ions and acrylamide. No tryptophyls in the native enzyme were accessible to I(-) and Cs(+), and 2.4 residues were accessible to acrylamide. Based on the crystallographic study, Trp154 is water-accessible, but it should be in a crevice not to contact with I(-) and Cs(+). All tryptophyls in the GdnHCl-denatured enzyme were exposed to the quenchers, while a considerable part was inaccessible in the urea-denatured one.

Metabolism of vitamin D(3) by human CYP27A1

Human vitamin D(3) 25-hydroxylase (CYP27A1) cDNA was expressed in Escherichia coli, and its enzymatic properties were revealed. The reconstituted system containing the membrane fraction prepared from the recombinant E. coli cells was examined for the metabolism of vitamin D(3). Surprisingly, at least eight forms of metabolites including the major product 25(OH)D(3) were observed. HPLC analysis and mass spectrometric analysis suggested that those metabolites were 25(OH)D(3), 26(OH)D(3), 27(OH)D(3), 24R,25(OH)(2)D(3), 1alpha, 25(OH)(2)D(3, )25,26(OH)(2)D(3) (25,27(OH)(2)D(3)), 27-oxo-D(3) and a dehydrogenated form of vitamin D(3). These results suggest that human CYP27A1 catalyzes multiple reactions and multiple-step metabolism toward vitamin D(3). The K(m) and V(max) values for vitamin D(3) 25-hydroxylation and 25(OH)D(3) 1alpha-hydroxylation were estimated to be 3.2 microM and 0.27 (mol/min/mol P450), and 3.5 microM and 0.021 (mol/min/mol P450), respectively. These kinetic studies have made it possible to evaluate a physiological meaning of each reaction catalyzed by CYP27A1.

Inhibitory effects of 1,4-naphthoquinone derivatives on rat cytochrome P4501A1-dependent monooxygenase activity in recombinant yeast microsomes

We reported previously that various naphthoquinone derivatives inhibited cytochrome P450-dependent monooxygenase of liver and placenta microsomes [Muto, N. et al. (1987) Biochem. Biophys. Res. Commun. 146, 487-494]. To understand the complex inhibitory behaviors that were observed, it is desirable to study the relationship between structure and inhibitory activity of naphthoquinones in a simplified system containing a single P450 species. In the present study, the inhibitory effects of six derivatives of 1,4-naphthoquinone (hereafter referred to as NQ) on rat cytochrome P4501A1-dependent 7-ethoxycoumarin O-deethylation were examined using yeast microsomes containing overexpressed rat P4501A1. Of these, 2-methyl-5-hydroxy-NQ, 2-methyl-NQ, 2-hydroxy-NQ, and NQ showed competitive inhibition, whereas 5,8-dihydroxy-NQ and 5-hydroxy-NQ showed noncompetitive inhibition. Judging from the inhibitor constant (K(i)), the binding affinity of the four competitive inhibitors for the substrate-binding pocket of P4501A1 is in the order: 2-CH(3)-5-OH-NQ > 2-CH(3)-NQ > NQ >> 2-OH-NQ. On binding with P4501A1, 2-CH(3)-5-OH-NQ, 2-CH(3)-NQ, and NQ induced distinct Type II, Type I, and reverse Type I spectra, respectively. These results indicate that methyl and hydroxyl groups introduced into NQ have unique effects on their binding mode and binding affinity.

Formation of the Ras dimer is essential for Raf-1 activation

Although it is well established that Ras requires membrane localization for activation of its target molecule, Raf-1, the reason for this requirement is not fully understood. In this study, we found that modified Ras, which is purified from Sf9 cells, could activate Raf-1 in a cell-free system, when incorporated into liposome. Using a bifunctional cross-linker and a protein-fragmentation complementation assay, we detected dimer formation of Ras in the liposome and in the intact cells, respectively. These results suggest that dimerization of Ras in the lipid membrane is essential for activation of Raf-1. To support this, we found that, when fused to glutathione S-transferase (GST), unprocessed Ras expressed in Escherichia coli could bypass the requirement for liposome. A Ras-dependent Raf-1 activator, which we previously reported (Mizutani, S., Koide, H., and Kaziro, Y. (1998) Oncogene 16, 2781-2786), was still required for Raf-1 activation by GST-Ras. Furthermore, an enforced dimerization of unmodified oncogenic Ras mutant in human embryonic kidney (HEK) 293 cells, using a portion of gyrase B or estrogen receptor, also resulted in activation of Raf-1. From these results, we conclude that membrane localization allows Ras to form a dimer, which is essential, although not sufficient, for Raf-1 activation.

Lysyl-tRNA synthetase of Bacillus stearothermophilus molecular cloning and expression of the gene

The gene of the lysyl-tRNA synthetase of Bacillus stearothermophilus NCA1503 was cloned and sequenced. The gene consists of 1485 bp nucleotides commencing with an ATG start codon and ending with a TAA stop codon, and encodes a polypeptide of 493 amino acids. The recombinant enzymes were expressed in E. coli using an expression plasmid containing the T7 RNA polymerase/promoter.

Activity of glucose-6-phosphate 1-dehydrogenase in hair follicles with male-pattern alopecia

Activity of glucose-6-phosphate 1-dehydrogenase (G6PDH) in human hair follicles was measured. A good relationship has been demonstrated between the activity and the ratio of the number of the anagen hairs to that of all the plucked hairs in the frontal-parietal region of the scalp with male-pattern alopecia. As the ratio becomes lower so that the advancing degree of alopecia is higher, the G6PDH activity becomes lower.

Refolding and recovery of recombinant human matrix metalloproteinase 7 (matrilysin) from inclusion bodies expressed by Escherichia coli

The recombinant prepro-form of human matrix metalloproteinase 7 (matrilysin or MMP-7) was overexpressed in Escherichia coli as insoluble inclusion bodies. The recombinant protein was refolded by 100-fold dilution after solubilization with 6 M guanidine HCl. The refolding was monitored by the recovery of matrilysin activity. The addition of either 1.0 M arginine or 0.1% Brij-35 promoted remarkably the refolding. The refolding was dependent on pH and temperature, with lower temperature (<10 degrees C) and pH 6-8 preferable. Glutathione had no effect on refolding, and it was excluded from the refolding conditions. Starting with inclusion bodies (2.0 g, wet) containing 360 mg protein, 29.5 mg of pro-matrilysin (30 kDa) was obtained after refolding with 1.0% Brij-35 at pH 7.5 and 4 degrees C for 12 h. Pro-matrilysin (24.0 mg) was purified to homogeneity by cation-exchange HPLC with a 15-fold increase in purity and an activity yield of 81.3%. Pro-matrilysin was converted entirely to matrilysin (19.0 kDa; 15.2 mg) by activation with a mercuric reagent. The activity (k(cat)/K(m)) of matrilysin was 1.7 x 10(5) M(-1) x s(-1).

No enzyme activity of 25-hydroxyvitamin D3 1alpha-hydroxylase gene product in pseudovitamin D deficiency rickets, including that with mild clinical manifestation

Pseudovitamin D deficiency rickets (PDDR) is an autosomal recessive disorder caused by defect in the activation of vitamin D. We recently isolated 25-hydroxyvitamin D3 1alpha-hydroxylase gene and identified four homozygous inactivating missense mutations in this gene by analysis of four typical cases of PDDR. This disease shows some phenotypic variation, and it has been suspected that patients with mild phenotypes have mutations that do not totally abolish the enzyme activity. To investigate the molecular defects associated with the phenotypic variation, we analyzed six additional unrelated PDDR patients: one with mild and five with typical clinical manifestation. By sequence analysis, all six patients were proven to have mutations in both alleles. The mutations varied, and we identified four novel missense mutations, a nonsense mutation, and a splicing mutation for the first time. The patient with mild clinical symptoms was compound heterozygous for T321R and a splicing mutation. The splice site mutation caused intron retention. Enzyme activity of the T321R mutant was analyzed by overexpressing the mutant 1alpha-hydroxylase in Escherichia coli cells to detect the subtle residual enzyme activity. No residual enzyme activity was detected in T321R mutant or in the other mutants. These results indicate that all of the patients, including those of mild phenotype, are caused by 1alpha-hydroxylase gene mutations that totally abolish the enzyme activity.

Enzymatic properties of human 25-hydroxyvitamin D3 1alpha-hydroxylase coexpression with adrenodoxin and NADPH-adrenodoxin reductase in Escherichia coli

We have cloned human 25-hydroxyvitamin D3 1alpha-hydroxylase cDNAs from normal subjects and patients with pseudovitamin D-deficient rickets (PDDR), and expressed the cDNAs in Escherichia coli JM109 cells. Kinetic analysis of normal 1alpha-hydroxylase in the reconstituted system revealed that Km values for 25(OH)D3 and (24R), 25(OH)2D3 were 2.7 and 1.1 microM, respectively. The lower Km value and higher Vmax/Km value for (24R),25(OH)2D3 indicated that it is a better substrate than 25(OH)D3 for 1alpha-hydroxylase. These results are quite similar to those of mouse 1alpha-hydroxylase. To establish a highly sensitive in vivo system, 1alpha-hydroxylase, adrenodoxin and NADPH-adrenodoxin reductase were coexpressed in E. coli cells. The recombinant E. coli cells showed remarkably high 1alpha-hydroxylase activity, suggesting that the electrons were efficiently transferred from NADPH-adrenodoxin reductase through adrenodoxin to 1alpha-hydroxylase in E. coli cells. Using this system, the activities of four mutants of 1alpha-hydroxylase, R107H, G125E, R335P and P382S, derived from patients with PDDR were examined. Although no significant reduction in expression of these mutants was observed, none showed detectable activity. These results strongly suggest that the mutations found in the patients with PDDR completely abolished 1alpha-hydroxylase activity by replacement of one amino acid residue.

Total synthesis of a natural antioxidant and structure-activity relationships of related compounds

A total synthesis of benzodioxole derivative 1 was achieved via a palladium(0)-catalyzed cross-coupling reaction in a 68% overall yield (4 steps). A novel series of benzodioxoles bearing a variety of aromatic and heterocyclic rings was also prepared and the antioxidative activity evaluated using in vitro model systems. Structure-activity studies revealed that i) intramolecular hydrogen-bonding in the phenol moiety reduced activity, ii) introduction of disubstituents at the ortho location relative to the phenol increased activity, and iii) the methylenedioxy function contributed to stabilization of the phenoxy radical. Among of these compounds, 5,7-di-(4-methoxyphenyl)-4-methoxy-6-hydroxy-1,3-benzodioxole (7p) was the most favorable agent and more potent than n-propyl gallate.