Alteration Of Catalytic Activity Research Articles

Vanadium and nickel deposition on FCC catalyst: Influence of residual catalyst acidity on catalytic products

Abstract The alteration of catalytic activity and selectivity of the cracking catalyst by porphyrinic metallic elements present in heavy crude oil fractions is a subject that requires serious attention. In this study, the effects of the two most deleterious of the metals (vanadium and nickel) and how they shift the product selectivity of the catalytic cracking are discussed, with a key focus on the catalytic behavior of the residual acidity consequent upon metal deactivation. Increasing loadings of vanadium and nickel were deposited on the FCC catalyst and subjected to a simulated FCC regeneration unit conditions. It is found that at loadings greater than 0.3 wt%, vanadium is 4–5 times as destructive as nickel on the crystalline structure of the catalyst. Catalytic evaluation results revealed correlations between residual surface acidity, catalyst activity and amount of coke formed on the catalyst at a constant catalyst-to-oil ratio (CTO). This result is in slight contrast with the widely reported enhanced coking activity of vanadium on FCC catalyst consequent upon dehydrogenation reaction. An alternative coke formation pathway based on the residual catalyst acidity is advanced for the observed coking behavior of high vanadium laden catalyst. In addition, a vanadium control measure relying on the acid-base chemistry and hydrothermal stability of a mixed-metal oxide is demonstrated as an effective method to limit the mobility of vanadium into the framework of the catalyst, the action that initiates vanadium deleterious effects. This study is expected to renew interest in the research on the coking behavior of metal poison catalysts.

Platelet Monoamine Oxidase Kinetics, Alcoholism Subtypes and Cigarette Smoking

In trying to dissociate the effect of alcohol and tobacco use on platelet monoamine oxidase-B (MAO-B) activity, we compared the enzyme kinetics in controls (n = 66) and alcohol-dependent patients (n = 81), subdivided according to the severity of both, alcohol and tobacco use. Platelet MAO-B kinetics was measured spectrophotofluorimetrically in chronic alcohol intoxication and after 3 weeks abstinence. In alcoholic patients, an increased Michaelis-Menten constant (16%, p < 0.01) was shown, notwithstanding smoking status. Maximal velocity did not differ between patients and controls when adjusted for smoking. In cigarette smokers, a highly significant dose-dependent reduction of platelet MAO velocity (40%, p < 0.001) was demonstrated, with a similar degree of reduction in patients and controls. Tobacco use itself had no influence on MAO affinity. No differences were shown between subtype 1 and 2 alcoholics, or between the day of admission and the 21st day of abstinence. In conclusion, it seems that both, alcohol and tobacco consumption, may contribute to the lowering of overall platelet MAO-B activity. The effect of alcohol is small, due to interference with substrate binding, and not alteration of catalytic activity. In contrast, the effect of cigarette smoking is pronounced and relates to the dose-dependent reduction of platelet MAO velocity, with no influence on its affinity.

Overexpression of Pin1 in non-small cell lung cancer (NSCLC) and its correlation with lymph node metastases

Pin1 isomerizes the bonds of molecules important for numerous oncogenic and cell-signaling pathways, including Bcl-2, p53, c-Jun, beta-catenin, NF-kappaB, cyclin D1, c-Myc and Raf-1. This can cause a change in conformation leading to alterations in catalytic activity, protein-protein interactions, subcellular localization and protein stability. These alterations have been shown to be associated with cell transformation and cancer progression. Pin1 is overexpressed in several different human cancers. This is the first report of Pin1 overexpression in clinical samples of non-small cell lung cancer (NSCLC). Protein expression levels of Pin1 in tumor and normal lung specimens were analyzed for expression of Pin1, cyclin D1, p53 and MDM2 using immunohistochemistry and compared to several clinicopathological characteristics. The mRNA expression of Pin1 was also analyzed using quantitative real-time RT-PCR and compared to clinicopathological characteristics. Pin1 protein was shown to be overexpressed in NSCLC tumor samples, and correlated with lymph node positive disease and tumor stage. High expression of MDM2 also correlated with lymph node positive disease and with poorly differentiated tumors. High expression of MDM2 also correlated with lymph node positive disease and with poorly differentiated tumors. High expression levels of Pin1 correlated with high levels of p53 or MDM2 protein, but did not show a correlation with cyclin D1. However, high levels of MDM2 correlated with cyclin D1 overexpression. Pin1 mRNA was expressed significantly more often in the tumors of smokers than of non-smokers. The relationship between the expression of protein and mRNA of Pin1 has obviously showed that protein expression isn't significantly associated with mRNA expression. Pin1 is overexpressed in many different cancers, including NSCLC, and may possibly be used as a tumor marker or as a target for cancer therapy.

The peptide methionine sulfoxide reductases, MsrA and MsrB (hCBS-1), are downregulated during replicative senescence of human WI-38 fibroblasts

In contrast to other oxidative modifications of amino acids, methionine sulfoxide can be enzymatically reduced back to methionine in proteins by the peptide methionine sulfoxide reductase system, composed of MsrA and MsrB. The expression of MsrA and one member of the MsrB family, hCBS-1, was analyzed during replicative senescence of WI-38 human fibroblasts. Gene expression decreased for both enzymes in senescent cells compared to young cells, and this decline was associated with an alteration in catalytic activity and the accumulation of oxidized proteins during senescence. These results suggest that downregulation of MsrA and hCBS-1 can alter the ability of senescent cells to cope with oxidative stress, hence contributing to the age-related accumulation of oxidative damage.

Alterations in catalytic activity and virus maturation produced by mutation of the conserved histidine residues of herpes simplex virus type 1 protease.

Mutant herpes simplex virus type 1 (HSV-1) viruses were constructed to characterize the roles of the conserved histidine residues (H61 and H148) of HSV-1 protease in the regulation of catalytic activity and virus maturation. Viruses containing mutations at H61 (H61V-V711, H61Y-V715, and H61A-V730) were unable to grow on Vero cells. These mutant viruses could process neither Pra to N0 nor ICP-35cd to ICP-35ef. Transmission electron microscopy studies of H61A-V730-infected Vero cells indicated that capsid maturation is arrested at a state characterized by the predominance of large symmetrical arrays of B capsids within the nucleus. Two mutations at H148 (in viruses H148A-V712 and H148E-V728) gave rise to mutant viruses that grew with a small-plaque phenotype; one of the viruses, H148E-V728, was particularly attenuated when grown at a low multiplicity of infection. The rate of processing of Pra to N0 in infected Vero cells increased in the order H148A-V712 < H148E-V728 < parental strain HSV-1-V731. The observation that H148A-V712 processes Pra to N0 and ICP-35cd to ICP-35ef, whereas H61A does not, establishes H61 as the catalytically essential conserved His assuming that HSV-1 protease, like other serine proteases, utilizes an active-site histidine residue in catalysis. Two of the mutations at H148 (viruses H148K-V729 and H148Y-V716) produced nonviable viruses. H148K-V729 processed neither Pra to N0 nor ICP-35cd to ICP-35ef, whereas H148Y-V716 processed Pra to N0 but did not process ICP-35cd to ICP-35ef. The range of phenotypes observed with the H148 mutant viruses suggests that residue 148 of the HSV-1 protease is a determinant of virus growth rate and viability because of its effects on the activity of the protease and/or the role of the protease domain in capsid assembly and DNA packaging.

INFLUENCE OF ETHANOL ADMINISTRATION ON THE ACTIVITY AND COMPARTMENTATION OF RAT LIVER MONOAMINE OXIDASES

Single-dose ethanol administration to rats caused inhibition of liver mitochondrial monoamine oxidases (MAO) A and B, and an increase in susceptibility of MAO A (but not MAO B) to limited proteolysis. Chronic ethanol feeding resulted in a less distinct alteration in catalytic activity and susceptibility to proteolysis of mitochondrial MAO, but increased the amount of soluble MAO. The sensitivity of membrane-bound MAO to inhibitors (imipramine and chlorpromazine), action of which depends on their lipophilicity and/or hydrophobicity, remained unchanged, compared with controls. Increased amounts of soluble MAO seen after chronic ethanol feeding probably reflect an impairment of insertion of newly synthesized enzyme molecules into the outer mitochondrial membrane, rather than solubilization of MAO from it.

Elimination of the Sensitivity of L-Aspartase to Active-Site-Directed Inactivation without Alteration of Catalytic Activity

The catalytic activity of the enzyme L-aspartase from Escherichia coli has previously been shown to be sensitive to sulfhydryl reagents. The use of group-specific reagents, and a sequence homology comparison study among the fumarase-aspartase family of enzymes, has not, however, lead to the identification of a specific, essential cysteinyl residue. We have recently shown that L-aspartate-beta-semialdehyde is an alternative substrate for L-aspartase, producing fumaric acid semialdehyde (FAA) which specifically inactivates the enzyme [Schindler, J. F., & Viola, R. E. (1994) Biochemistry 33, 9365]. Proteolytic digests of the resulting inactivated enzyme have now been mapped by HPLC and mass spectrometry. A specific residue (Cys-273) has been determined to be the site of FAA modification. Site-directed mutagenesis of this cysteine in the E. coli enzyme has produced altered enzymes which are considerably less sensitive to active-site-directed inactivation, while retaining full catalytic activity. Thus, cysteine-273 has been identified as an active-site nucleophile that, while not directly involved in catalysis in L-aspartase, is poised to attack an activated double bond in an enzyme-bound product analogue.

Effect of diabetes mellitus on responses of the rat basilar artery to activation of beta-adrenergic receptors

The goal of this study was to determine whether diabetes mellitus alters reactivity of the basilar artery in vivo to activation of beta-adrenergic receptors. We measured diameter of the basilar artery in non-diabetic and diabetic (streptozotocin 50–60 mg/kg i.p.) rats during superfusion with isoproterenol and norepinephrine, which dilate cerebral blood vessels via activation of beta-adrenergic receptors. Dilatation of the basilar artery in response to isoproterenol and norepinephrine was significantly less in diabetic compared to non-diabetic rats. To determine whether dmpaired dilatation of the basilar artery in diabetic rats in response to isoproterenol and norepinephrine was related to an alteration in catalytic activity of adenylate cyclase, we examined dilatation of the basilar artery in response to forskolin, a direct activator of adenylate cyclase. In contrast to that observed for isoproterenol and norepinephrine, forskolin produced similar dilatation of the basilar artery in non-diabetic and diabetic rats. Thus, the findings of the present study suggest that diabetes mellitus impairs dialtation of the basilar artery in vivo in response to activation of beta-adrenergic receptors. In addittion, impairment of beta-adrenergic mediated dilatation of the basilar artery during diabetes mellitus does not appear to be related to an alteration in catalytic activity of adenylate cyclase.

Alterations of the microsomal glucose-6-phosphatase system evoked by ferrous iron- and haloalkane free-radical-mediated lipid peroxidation

Alterations of catalytic activities of the microsomal glucose-6-phosphatase system were examined following either ferrous iron- or halothane (CF 3CHBrCl) and carbon tetrachloride (CCl 4) free-radical-mediated peroxidation of the microsomal membrane. Enzyme assays were performed in native and solubilized microsomes using either glucose 6-phosphate or mannose 6-phosphate as substrate. Lipid peroxidation was assessed by the amounts of malondialdehyde equivalents formed. Regardless of whether the experiments were performed in the presence of NADPH/Fe 3+, NADPH/CF 3CHBrCl, or NADPH/CCI 4, with the onset of lipid peroxidation, mannose-6-phosphatase activity of the native microsomes increased immediately, while further alterations in catalytic activities were only detectable when lipid peroxidation had passed characteristic threshold values: above 2 nmol malondialdehyde/mg microsomal protein, glucose-6-phosphatase activity of the native microsomes was lost, and at 10 nmol malondialdehyde//mg microsomal protein, glucose-6-phosphatase and mannose-6-phosphatase activity of the solubilized microsomes started to decline. It is concluded that the latter alterations are due to an irreversible damage of the phosphohydrolase active site of the glucose-6-phosphatase system, while the changes observed at earlier stages of microsomal lipid peroxidation may also reflect alterations of the transporter components of the glucose-6-phosphatase systems. Virtually no changes in the catalytic activities of the glucose-6-phosphatase system occurred under anaerobic conditions, indicating that .CF 3CHCl and .CCl 3 radicals are without direct damaging effect on the glucose-6-phosphatase system. Further, maximum effects of carbon tetrachloride and halothane on lipid peroxidation and enzyme activities were observed at an oxygen partial pressure ( P o 2 ) of 2 mmHg, providing additional evidence for the crucial role of low P o 2 in the hepatotoxicity of both haloalkanes.

Regulation of the synthesis of tyrosine aminotransferase: the relationship to mRNATAT.

The activity of the hepatic enzyme tyrosine aminotransferase (TAT) is the sum of many diverse regulatory factors. These include the developmental stage of the animal, the hormonal and nutritional environment of the animal (or tissue culture cell), other extrinsic and intrinsic regulatory cycles and factors (including cytoplasmic substances), and chromatin structure. Although TAT is subject to a number of post-translational modifications, alterations in catalytic activity always parallel changes in enzyme amount. In a few instances this is due to a selective change in TAT degradation, but most are due to changes in the rate of aminotransferase synthesis. Recent studies have shown that TAT synthesis is generally directly correlated with the activity, and presumably amount, of the mRNA that codes for tyrosine aminotransferase.

Allosteric serine hydroxymethyltransferase from monkey liver: Correlation of conformational changes caused by denaturants with the alterations in catalytic activity

The far-ultraviolet region circular dichroic spectrumof serine hydroxymethyltransferase from monkey liver showed that the protein is in an α-helical conformation. The near ultraviolet circular dichoric spectrum revealed two negative bands originating from the tertiary conformational environment of the aromatic amino acid residues. Addition of urea or guanidinium chloride perturbed the characteristic fluorescence and far ultraviolet circular dichroic spectrum of the enzyme. The decrease in (θ)222 and enzyme activity followed identical patterns with increasing concentrations of urea, whereas with guanidinium chloride, the loss of enzyme activity preceded the loss of secondary structure. 2-Chloroethanol, trifluoroethanol and sodium dodecyl sulphate enhanced the mean residue ellipticity values. In addition, sodium dodecyl sulphate also caused a perturbation of the fluorescence emission spectrum of the enzyme. Extremes of pH decreased the — (θ)222 value. Plots of — (θ)222and enzyme activity as a function of pH showed maximal values at pH 7.4–7.5. These results suggested the prevalence of “conformational flexibility” in the structure of serine hydroxymethyltransferase.