Inactivation and conformational changes of fatty acid synthase from chicken liver during unfolding by sodium dodecyl sulfate

Fatty acid synthase is an important enzyme participating in energy metabolism in vivo. The inactivation and conformational changes of the multifunctional fatty acid synthase from chicken liver in SDS solutions have been studied. The results show that the denaturation of this multifunctional enzyme by SDS occurred in three stages. At low concentrations of SDS (less than 0.15 mM) the enzyme was completely inactivated with regard to the overall reaction. For each component of the enzyme, the loss of activity occurred at higher concentrations of SDS. Significant conformational changes (as indicated by the changes of the intrinsic fluorescence emission and the ultraviolet difference spectra) occurred at higher concentrations of SDS. Increasing the SDS concentration caused only slight changes of the CD spectra, indicating that SDS had no significant effect on the secondary structure of the enzyme. The results suggest that the active sites of the multifunctional fatty acid synthase display more conformational flexibility than the enzyme molecule as a whole.

Inactivation and conformational changes of yeast alcohol dehydrogenase in trifluoroethanol solutions

Conformational changes of yeast alcohol dehydrogenase in trifluoroethanol solutions have been followed by fluorescence emission and circular dichroism spectroscopy. At low concentration (less than 5%), trifluoroethanol shows a reversible inhibition competitive to ethanol and noncompetitive to NAD+. The inhibition constants for native and structural-zinc-removed yeast alcohol dehydrogenase were 5.8 and 1.1 mM, respectively, suggesting that the active site becomes more flexible after the structural zinc is removed. At higher trifluoroethanol concentrations the enzyme was irreversibly inactivated. Comparison of inactivation and conformational changes of yeast alcohol dehydrogenase denatured in trifluoroethanol solutions shows that the extent of inactivation is larger than the extent of conformational changes at the same trifluoroethanol concentration. The results obtained from circular dichroism spectra show that the presence of trifluoroethanol can induce the formation of secondary structure of the enzyme.

Dissociation of creatine kinase under different denaturation conditions

Dissociation of dimeric creatine kinase under different denaturation conditions was investigated using the cleavable cross-linker 3, 3;-dithiobis(succinimidyl propionate). The results show that at low denaturant concentrations or at low denaturation temperatures the creatine kinase was mostly inactivated, but the enzyme was still either in the dimeric state or very slightly dissociated. It appears, therefore, that for several denaturation conditions, inactivation of the enzyme is not due to the dissociation of the active dimer.

Reactivation kinetics of 5,5'-dithiobis-(2-nitrobenzoic acid)-modified creatine kinase reactivated by dithiothreitol

The reduction of 5,5'-dithiobis-(2-nitrobenzoic acid)-modified creatine by dithiothreitol has been studied using the kinetic theory of the substrate reaction during modification of enzyme activity as previously described by C.L. Tsou (Adv. Enzymol. Rel. Areas Mol. Biol. 61 (1988) 381-436). The results show that the modified creatine kinase can be fully reactivated by an excess concentration of dithiothreitol in a monophasic kinetic course. The presence of ATP or the transition-state analogue markedly slows the apparent reactivation rate constant, while creatine shows no effect. The substrates creatine-ADP-Mg2+ can induce conformational changes of the modified enzyme but adding NO-3 cannot induce further changes that occur with the native enzyme. The reactive cysteines' location and role in the catalysis of creatine kinase are discussed. It is suggested that the cysteine may be located in the hinge area of the two domains of creatine kinase. The reactive cysteine of creatine kinase may play an important role not in the binding to the transition-state analogue but in the conformational changes caused by the transition-state analogue.

An essential lysine residue of green crab (Scylla Serrata) alkaline phosphatase

The values of pKa (10.38) and Hion (10.92 Kcal/mol) have been determined for the ionizing groups controlling activity of green crab alkaline phosphatase. The results suggest that -NH2 of lysine residue responsible for the ionization with pKc = 10.38 and delta H(o)ion = 10.92 Kcal/mol is in the active site of the enzyme. Modification of lysine residues of the enzyme by an excess of 2,4,6-trinitrobenzenesulfonic acid leads to complete inactivation. The two results coincide with each other. Quantitative assessment of the data indicates that among the reactive -NH2 groups modified only one is essential for the activity of the enzyme.

Inactivation of succinate-ubiquinone reductase in substrate mixture

Succinate-ubiquinone reductase plays an important role in the respiratory chain. Previous work showed that preparation of succinate-ubiquinone reductase was relatively stable. Though the enzyme catalysis has been extensively studied, the inactivation of succinate-ubiquinone reductase has never been reported. In the present study, the kinetic theory of the substrate reaction of irreversible inhibition described by Tsou (Adv. Enzymol. Relat. Areas Mol. Biol. 61 (1988) 381-436) was applied to study the course of an unexpected slow inactivation of succinate-ubiquinone reductase in the substrate assay mixture containing different concentrations of substrates, succinate and 2,6-dichloroindophenol. The results showed that the inactivation of succinate-ubiquinone reductase in the substrate mixture is a first order reaction. The inactivation rate decreased with increasing concentration of succinate. The values of the micro rate constants for free and succinate bound enzyme were 0.22 +/- 0.01 and 0.052 +/- 0.002 min-1, respectively. Binding with 2-thenoyl-trifluroacetone, a inhibitor specially for the quinone binding site, slowed down the inactivation. However, the rate of inactivation did not change with increasing 2,6-dichloroindophenol concentration. The study showed that succinate-ubiquinone reductase was irreversibly inactivated in the substrate mixture. The results suggest that the inactivation was not due to dilution or dissociation of the enzyme, nor to complete usage of the substrate, inhibition of the yielded product or some possible trace component in the substrate mixture, nor to modification of the essential thiol group in the succinate binding site of succinate-ubiquinone reductase. The enzyme became more stable after binding with succinate.

Kinetics of inhibition of Penaeus penicillatus acid phosphatase by bromoacetic acid

The kinetics of inhibition of penaeus penicillatus acid phosphatase by bromoacetic acid has been studied. The results show that inhibition of the enzyme by bromoacetic acid is a slow, reversible reaction. The microscopic rate constants for the reaction of inhibitor with the enzyme were determined. The presence of the substrate offers marked protection of this enzyme against inhibition by bromoacetic acid. The above results suggest that the histidine residue is essential for activity and are situated at the active site of the enzyme.

Kinetics of slow reversible inhibition of human muscle creatine kinase by planar anions

The toxicity of NO3- and NO2- to mammals has been widely publicized. However, the kinetic mechanism of inhibition of human muscle creatine kinase by NO3- and NO2- has not been explored. The kinetic theory of the substrate reaction during the modification of enzyme activity previously described by Tsou (Adv. Enzymol. Related Areas Mol. Biol. 1988, 61, 381-436) has been applied to a study of the kinetics of slow reversible inhibition of human muscle creatine kinase by planar anions (NO3- and NO2-). The kinetic equation of the substrate reaction was derived from theoretical analysis and experimental data, then simplified. The microscopic rate constants for the reaction of the inhibitors with the enzyme were obtained from the simplified equation for the substrate reaction in the presence of the inhibitors. The results show that the apparent forward rate constant A is dependent on ATP concentration, indicating competition between the inhibitor (NO3- or NO2-) and ATP. The results also suggest that binding of creatine-MgADP and the anion with the enzyme is very tight, since their binding constants are much higher than those for normal substrates.

Alkaline-induced unfolding and salt-induced folding of pig heart lactate dehydrogenase under high pH conditions

The alkaline-induced unfolding and the salt-induced folding of pig heart lactate dehydrogenase under high pH conditions have been followed by fluorescence emission spectra and circular dichroism spectra. The results for alkaline-induced denaturation of lactate dehydrogenase show that at low ionic strength, increasing the pH value increased the extent of unfolding of the enzyme to the maximum ultimate unfolded conformation at about pH 13.0. At pH 12.5, although the enzyme was completely inactivated, most of the ordered structure was retained. Even at pH 13.5, the apparently fully unfolded enzyme still retained some ordered secondary structure. Kinetic analysis showed that at high pH, the inactivation rate constants of the enzyme are an order of magnitude faster than the unfolding rate constants at least. The above results are in accord with the suggestion by Tsou (Trends Biochem Sci 1986;11:427-429 and Science 1993;262:380-381) that the active site is usually more flexible than the enzyme molecule. At pH 13.0, adding salt to the solution caused the relatively unfolded state of the denatured enzyme to change into a compact conformational state by hydrophobic collapsing. The folded state induced by the salt bound ANS strongly, indicating the existence of an increased hydrophobic surface. The above results suggest that the salt-induced folded state at high pH may be the folded intermediate which exists in the general protein folding and that the large residual ordered secondary structure might become folded during the salt-induced folding.

Inactivation of creatine kinase is due to the conformational changes of the active sites during thermal denaturation

The conformational changes of the active site of creatine kinase (ATP: creatine N-phosphotransferase EC 2.7.3.2.) during thermal denaturation was followed by changes in fluorescence at the active site of the enzyme labeled by o-phthalaldehyde. Conformational changes of the active site occurred at the same time as inactivation of the enzyme. The active site changes occurred before the denaturation of the enzyme molecule as a whole was detected. The above results showed that the thermal inactivation of the creatine kinase was due to the conformational changes of its active sites.

Kinetics of inactivation of Penaeus penicillatus acid phosphatase during inhibition by N-bromosuccinimide

In the present investigation, the inactivation by N-bromosuccinimide of acid phosphatase from penaeus penicillatus has been studied using the kinetic method of the substrate reaction during modification of enzyme activity as previously described by Tsou [(1988, Adv. Enzymemol. Related Areas Mol. Biol. 61, 381-436]. The results show that inactivation of the enzyme by N-bromosuccinimide is a slow, reversible reaction. The results also clearly show that the modification of the tryptophan residues of penaeus penicillatus acid phosphatase by high concentrations of N-bromosuccinimide led to the complete inactivation of the enzyme. The microscopic rate constants were determined for the reaction of the inactivator with the free enzyme and with the enzyme-substrate complex. Comparison of the obtained microscopic rate constants indicates that the presence of the substrate offers marked protection of the enzyme against inactivation by N-bromosuccinimide. The above results suggest that the tryptophan residue is essential for activity and may be situated at the active site of the enzyme.

The effects of N-thiophosphoryl amino acids on the activity of green crab (Scylla Serrata) alkaline phosphatase

Green crab (Scylla Serrata) alkaline phosphatase (EC 3.1.3.1) is a metalloenzyme which catalyzed the nonspecific hydrolysis of phosphate monoesters. In the present paper, the effects of several N-thiophosphoryl amino acids on the activity of green crab alkaline phosphatase have been studied. The results show that these derivatives of amino acids can lead to reversible inactivation. The equilibrium constants for inhibitors binding with the enzyme and/or the enzyme-substrate complexes have been determined. The obtained results show that both N-thiophosphoryl-Cys and N-thiophosphoryl-Glu were non-competitive inhibitors, while other five N-thiophosphoryl amino acids were un-competitive inhibitors. For the un-competitive inhibitors, the inhibition strength follows the order N-thiophosphoryl-Ile > -Val > -Lys > -Ala > -Tyr. Compared with respective free amino acids, it can be seen that N-thiophosphorylation of the amino acids increased their inhibition strength except the N-thiophosphoryl-Cys.

Comparison of inactivation and conformational changes of native and apo yeast alcohol dehydrogenase during thermal denaturation

The conformational changes of native and apo yeast alcohol dehydrogenase during thermal denaturation have been followed by fluorescence emission and circular dichroism spectra. A comparison of inactivation and conformational changes during thermal denaturation shows that for the native enzyme and for the apo-I YADH which has the conformational zinc removed, the extent of inactivation was larger than the extent of conformational changes at the same temperature. This result supported the suggestion by Tsou (Trends Biochem. Sci. 1986, 11, 427-429: Science 1993, 262, 380-381) that the enzyme active site is more flexible. The results also show that apo-I YADH without the conformational zinc was more easily inactivated with increasing incubation temperature, indicating that the stability of the apo-I YADH decreased. Kinetic analysis suggest that the substrate does not provide any protective effect during thermal inactivation of native and apo-I YADH.

Inactivation and conformational changes of yeast invertase during unfolding in urea and guanidinium chloride solutions

Yeast invertase exists in two different forms. The cytoplasmic enzyme is non-glycosylated, whereas the external invertase contains approximately 50% carbohydrate of the high mannose type. In this paper, the inactivation and the conformational changes of the yeast external invertase are analyzed for unfolding in urea and guanidinium chloride. The results show that much lower concentrations of denaturants are required to bring about inactivation than are required to produce significant conformational changes of the yeast external invertase. The results suggest that the active sites of the external invertase containing carbohydrate residues may display more conformational flexibility than the enzyme molecules as a whole.

Conformational changes of creatine kinase in trifluoroethanol solutions

The conformational changes of creatine kinase (ATP:creatine N-phosphotransferase, EC 2.7.3.2) in trifluoroethanol solutions have been followed by fluorescence emission and circular dichroism spectra. At low trifluoroethanol concentrations, less than 15%, the enzyme was completely inactivated with no observed marked conformational changes. The fluorescence emission maximum of the native enzyme was at 337 nm. With increasing trifluoroethanol concentration, the fluorescence emission maximum red-shifted in magnitude to a maximum value (355 nm) at 40% trifluoroethanol, indicating that the tryptophan residues were completely exposed. The results obtained from CD spectra show that the presence of trifluoroethanol can induce the formation of secondary structure in the native enzyme and in urea-denatured enzyme.

The essential tryptophan residues of pig kidney aminoacylase

The tryptophan residues in pig kidney aminoacylase (N-acylamino acid amido hydrolase, EC 3.5.1.14) have been modified by N-bromosuccinimide (NBS) at low pH. The modification of eight tryptophan residues as measured by spectrophotometric and spectrofluorimetric methods leads to complete loss of enzymatic activity. The decreases in absorption at 280 nm and fluorescence emission at 337 nm indicate the modification of tryptophan residues. Both the inactivation and tryptophan residual modification are monophasic, first-order reactions. Quantitative treatment of the data (Tsou, C. L., Sci. Sin., 1962, 11, 1535-1558) shows that among the tryptophan residues modified, two are essential for aminoacylase catalytic activity. Kördel and Schneider (Hoppe-Seyler's Physiol. Chem. 1976, 357, 1109-1115) reported that the modification of tryptophan residues led to inactivation of aminoacylase, and suggested that tryptophan residues are essential for enzymatic activity. We have now shown that eight tryptophan residues can be modified by N-bromosuccinimide and that two of them are essential for the catalytic activity of this enzyme.

Cytoplasmic creatine kinases from giant pandas

The muscle and brain creatine kinases of giant panda have been isolated and purified. The purified muscle and brain enzymes (MM and BB) are homogeneous on both the polyacrylamide gel electrophoresis in the presence and absence of SDS. Both enzymes are dimers, consisting of two identical subunits each with a molecular weight of 42,000 daltons. The characteristics of muscle and brain enzymes have been studied, respectively. The hybridized enzyme, MB, was prepared by hybridization of MM and BB. The kinetic parameters of MM, BB and MB were determined, respectively. The results from modification of SH groups show that the SH groups of panda creatine kinases are essential for their activity and among the all SH groups in the enzyme only one per subunit is essential for enzymatic activity.

Kinetics of thermal inactivation of lactate dehydrogenase from rabbit muscle

The kinetics of thermal inactivation of rabbit muscle lactate dehydrogenase at different temperatures has been studied using the kinetic method for the substrate reaction during irreversible inhibition of enzyme activity previously described by Tsou [Adv. Enzymol. Relat. Areas Mol. Biol. (1988), 61, 381-436]. The results show that thermal inactivation of the enzyme is an irreversible reaction. Microscopic rate constants were determined for thermal inactivation of the free enzyme and the enzyme-substrate complex. The inactivation rate constant of the free enzyme is much larger than the rate constant of the enzyme-substrate complex. The results suggest that the presence of the substrate has a certain protective effect against thermal inactivation of the enzyme.

Comparison of inactivation and unfolding of yeast alcohol dehydrogenase during thermal denaturation

It has been reported that inactivation occurs before noticeable conformational change can be detected during denaturation of creatine kinase (ATP:creatine N-phosphotransferase, EC 2.7.3.2) and other enzymes by guanidinium chloride or urea. It has therefore been suggested that enzyme active sites may display more conformational flexibility than the enzyme molecules as a whole. The present paper compares the inactivation and unfolding of yeast alcohol dehydrogenase during thermal denaturation. Under identical conditions, inactivation takes place before noticeable conformational changes. Kinetics of unfolding can be resolved into two phases. For a given temperature, the fast phase rates are about one order of magnitude slower than the inactivation rates of the free enzyme and approximately the same magnitude as the inactivation rates of enzyme-substrate complexes. This is general accord with the suggestion made previously by Tsou, indicating that the active sites of metal enzymes are situated in a region more flexible than the molecules as a whole.

Unfolding and inactivation of Penaeus penicillatus acid phosphatase during denaturation by guanidine hydrochloride

The conformational changes of penaeus penicillatus acid phosphatase during denaturation in guanidine hydrochloride solutions were studied by following changes in the intrinsic fluorescence, ultraviolet difference absorption, and circular dichroism spectra. Inactivation of the enzyme in guanidine hydrochloride solutions were compared with unfolding of the enzyme molecule. The results show that the extent of unfolding in guanidine solutions measured by several different methods closely coincide with each other and that slightly lower concentrations of guanidine are required to bring about inactivation than are required to produce significant conformational changes of the enzyme molecule. At the same concentrations, the inactivation rate constants are markedly faster than the rate constants for unfolding of the enzyme. The above results suggest that the active sites of this enzyme display more conformational flexibility than the enzyme molecule as a whole.

Kinetics of irreversible inhibition of yeast alcohol dehydrogenase during modification by 4,4'-dithiodipyridine

The course of inactivation of yeast alcohol dehydrogenase (YADH) using 4,4'-dithiodipyridine (DSDP) has been studied in this paper. The results show that the reaction mechanism between DSDP and YADH is a competitive, complexing inhibition. The microscopic constants for the inactivation of the free enzyme and the enzyme-substrate complex were determined. The presence of the substrate NAD+ offers strong protection for this enzyme against inactivation by DSDP. The above results suggest that two Cys residues are essential for activity and are situated at the active site. These essential Cys residues should be Cys-46 and Cys-174 which are ligands to the catalytic zinc ion. Another Cys residue, which can be modified by DSDP, is non-essential for activity of the enzyme.

Kinetics of the thermal inactivation of alkaline phosphatase from green crab (Scylla serrata)

The kinetics of thermal inactivation of alkaline phosphatase from green crab (Scylla Serrata) has been studied using the kinetic method relating to the substrate reaction during irreversible inhibition of enzyme activity previously described by Tsou. The results show that the thermal inactivation of the enzyme is an irreversible reaction. Comparison of the microscopic rate constants for thermal inactivation of free enzyme and the enzyme-substrate complex shows that the presence of substrate has a certain protective effect against thermal inactivation.

Catalysis of the refolding of urea denatured creatine kinase by peptidyl-prolyl cis-trans isomerase

The effect of peptidyl-prolyl cis-trans isomerase (PPIase) on the refolding and reactivation courses of urea-denatured creatine kinase was followed by fluorescence emission, ultraviolet difference spectra and recovery of activity. PPIase is shown to accelerate the slow-phasic reaction of the refolding of urea-denatured creatine kinase. The results suggest that the prolyl peptide bond isomerization may be one of the rate-determining steps in the refolding of creatine kinase.

Repair of thyroid cartilage defect with bone morphogenetic protein

The object of this research was to investigate whether a thyroid cartilage defect can be repaired by newly formed bone induced by bovine bone morphogenetic protein (bBMP). Bilateral thyroid cartilage defects measuring 0.5 x 0.6 cm were created in 25 adult rabbits. Experimental defects were implanted with ceramic bone particles combined with bBMP, or in controls, without bBMP. The animals were painlessly killed at 2, 4, 8, 12 and 16 weeks after implantation. The tissue responses were analyzed by routine histologic examination. An increase in the amount of new bone was observed in the interval from 4 to 12 weeks, and the defects were completely filled with new bone at 16 weeks, in contrast to a minimal new cartilage formation at the defect edges in controls. The results indicate that cartilage defects can be repaired by inducing new bone formation from mesenchymal cells in both perichondrium and muscular fascia.

An essential tryptophan residue of green crab (syclla serrata) alkaline phosphatase

The tryptophan residues in green crab (scylla serrata) alkaline phosphatase (EC 3.1.3.1) have been modified by N-bromosuccinimide (NBS). The modification of five tryptophan residues leads to complete loss of enzymatic activity. With the increase of NBS concentration, both the absorption at 278 nm and the fluorescence emission intensity at 335 nm of the modified enzyme decreased markedly indicating the modification of tryptophan residues. Quantitative treatment of the data (Tsou, Sci. Sinica 1962, 11, 1535-1558) shows that among the tryptophan residues modified, one is essential for its catalytic activity. The presence of the substrate markedly protects the modification of tryptophan residues as well as the inactivation, suggesting that the essential tryptophan residue is situated at the active site of this enzyme.