Reaction of the anionic acetylation agent methyl acetyl phosphate with D-3-hydroxybutyrate dehydrogenase

1986 ◽  
Vol 64 (5) ◽  
pp. 434-440 ◽  
Author(s):  
Ronald Kluger ◽  
Wing-Cheong Tsui
Keyword(s):  
Ph Dependence ◽  
Competitive Inhibitor ◽  
Amino Group ◽  
Acetyl Phosphate ◽  
Hydrogen Bond Donor ◽  
Phosphate Monoesters ◽  
Dimethylmaleic Anhydride ◽  
A Site ◽  
Acyl Phosphate ◽  
Kinetics Of

Methyl acetyl phosphate is a competitive inhibitor of the reduction of acetoacetate by D-3-hydroxybutyrate dehydrogenase. The material also irreversibly inactivates the enzyme. The kinetics of the inactivation are consistent with methyl acetyl phosphate acetylating the conjugate base of a hydrogen bond donor. Protection offered by a substrate analogue (methyl acetonylphosphonate) in the presence of coenzyme implicates reaction at the cationic active site. Reversible protection by the amino group reagent 2,3-dimethylmaleic anhydride suggests that methyl acetyl phosphate reacts with an amino group. Sulfhydryl reagents and acetyl phosphate, a poorer acetylating agent, do not inactivate the enzyme. The pH dependence of the inactivation suggests that the acetylation occurs at a site that has a pKa of 8.2. The utility of methyl acetyl phosphate and other acyl phosphate monoesters in reacting with lysines adjacent to cationic sites of enzymes, hemoglobin, and histones is noted.

scholarly journals Studies of the specificity and kinetics of rat liver spermidine/spermine N1-acetyltransferase

1983 ◽  
Vol 213 (3) ◽  
pp. 701-706 ◽  
Author(s):  
F Della Ragione ◽  
A E Pegg
Keyword(s):  
Rat Liver ◽  
Kinetic Mechanism ◽  
Competitive Inhibitor ◽  
Aliphatic Chain ◽  
Amino Group ◽  
Acetyl Coa ◽  
Competitive Kinetics ◽  
Primary Amino ◽  
Secondary Amino ◽  
Kinetics Of

The substrate specificity and kinetic mechanism of spermidine N1-acetyltransferase from rat liver was investigated using a highly purified (18 000-fold) preparation from the livers of rats in which the enzyme was induced by treatment with carbon tetrachloride (1.5 ml/kg body wt. 6h before death). The enzyme catalysed the acetylation of spermidine, spermine, sym-norspermidine, sym-norspermine, N-(3-aminopropyl)-cadaverine, N1-acetylspermine, 3,3′-diamino-N-methyldipropylamine and 1,3-diaminopropane, but was inactive with putrescine, cadaverine, sym-homospermidine and N1-acetylspermidine. These results suggest that the enzyme is highly specific for the acetylation of a primary amino group that is separated by a three-carbon aliphatic chain from another nitrogen atom (i.e. the substrates are of the type H2N[CH2]3NHR). The maximal rates of acetylation of 1,3-diaminopropane and 3,3′-diamino-N-methyldipropylamine were much lower than the maximal rates with spermidine or sym-norspermidine as substrates, suggesting a preference for a secondary amino group bearing the aminopropyl group that is acetylated. The best substrates for acetylation were sym-norspermidine and sym-norspermine, which had Km values of about 10 micrograms and Vmax. values of about 2 mumol of product/min per mg of enzyme compared with Km of 130 microM and Vmax. of 1.3 mumol/min per mg for spermidine. N1-Acetylspermidine (the product of the reaction) and N8-acetylspermidine were weak inhibitors and were competitive with spermidine, having Ki values of about 6.6 mM and 0.4 mM respectively. N1-Acetylspermidine was a non-competitive inhibitor with respect to acetyl-CoA. CoA was also inhibitory to the reaction, showing non-competitive kinetics when either [acetyl-CoA] or [spermidine] was varied. These results suggest that the reaction occurs via an ordered Bi Bi mechanism in which spermidine binds first and N1-acetyl-spermidine is the final product to be released.

Kinetic Aspects of the Interaction of Blood Clotting Enzymes

1968 ◽  
Vol 19 (03/04) ◽  
pp. 364-367 ◽  
Author(s):  
H. C Hemker ◽  
P. W Hemker
Keyword(s):  
Enzyme Kinetics ◽  
Blood Clotting ◽  
Competitive Inhibition ◽  
Competitive Inhibitor ◽  
Kinetics Of

SummaryThe enzyme kinetics of competitive inhibition under conditions prevailing in clotting tests are developed and a method is given to measure relative amounts of a competitive inhibitor by means of the t — D plot.

scholarly journals Hydrogen exchange kinetics of human hemoglobins. The pH dependence of solvent accessibility in cyanomet-, oxy-, and deoxyhemoglobin.

1978 ◽  
Vol 253 (10) ◽  
pp. 3702-3707
Author(s):  
B.E. Hedlund ◽  
P.E. Hallaway ◽  
B.E. Hallaway ◽  
E.S. Benson ◽  
A. Rosenberg
Keyword(s):  
Hydrogen Exchange ◽  
Solvent Accessibility ◽  
Ph Dependence ◽  
Exchange Kinetics ◽  
Kinetics Of

Dual kinetics of OATP2B1: Inhibitory potency and pH-dependence of OATP2B1 inhibitors

2021 ◽  
pp. 100416
Author(s):  
Ryo Sato ◽  
Takeshi Akiyoshi ◽  
Tokio Morita ◽  
Kazuhiro Katayama ◽  
Kodai Yajima ◽  
...  
Keyword(s):  
Ph Dependence ◽  
Inhibitory Potency ◽  
Kinetics Of

Impact of pH on growth of Staphylococcus epidermidis and Staphylococcus aureus in vitro

2021 ◽  
Vol 70 (9) ◽  
Author(s):  
Vidula Iyer ◽  
Janhavi Raut ◽  
Anindya Dasgupta
Keyword(s):  
Staphylococcus Aureus ◽  
Growth Kinetics ◽  
Staphylococcus Epidermidis ◽  
Type Species ◽  
Ph Dependence ◽  
Skin Microbiome ◽  
Content Type ◽  
Link Type ◽  
Kinetics Of

The pH of skin is critical for skin health and resilience and plays a key role in controlling the skin microbiome. It has been well reported that under dysbiotic conditions such as atopic dermatitis (AD), eczema, etc. there are significant aberrations of skin pH, along with a higher level of Staphylococcus aureus compared to the commensal Staphylococcus epidermidis on skin. To understand the effect of pH on the relative growth of S. epidermidis and S. aureus , we carried out simple in vitro growth kinetic studies of the individual microbes under varying pH conditions. We demonstrated that the growth kinetics of S. epidermidis is relatively insensitive to pH within the range of 5–7, while S. aureus shows a stronger pH dependence in that range. Gompertz’s model was used to fit the pH dependence of the growth kinetics of the two bacteria and showed that the equilibrium bacterial count of S. aureus was the more sensitive parameter. The switch in growth rate happens at a pH of 6.5–7. Our studies are in line with the general hypothesis that keeping the skin pH within an acidic range is advantageous in terms of keeping the skin microbiome in balance and maintaining healthy skin.

Kinetics of the oxidation of reduced nicotinamide adenine dinucleotide by horseradish peroxidase compounds I and II

1986 ◽  
Vol 64 (4) ◽  
pp. 323-327 ◽  
Author(s):  
Mohammed A. Kashem ◽  
H. Brian Dunford
Keyword(s):  
Horseradish Peroxidase ◽  
Active Site ◽  
Nicotinamide Adenine Dinucleotide ◽  
Ph Dependence ◽  
Transient State ◽  
Nicotinamide Adenine ◽  
Compound I ◽  
Single Ionization ◽  
Reduced Nicotinamide Adenine Dinucleotide ◽  
Kinetics Of

The transient state kinetics of the oxidation of reduced nicotinamide adenine dinucleotide (NADH) by horseradish peroxidase compound I and II (HRP-I and HRP-II) was investigated as a function of pH at 25.0 °C in aqueous solutions of ionic strength 0.11 using both a stopped-flow apparatus and a conventional spectrophotometer. In agreement with studies using many other substrates, the pH dependence of the HRP-I–NADH reaction can be explained in terms of a single ionization of pKa = 4.7 ± 0.5 at the active site of HRP-I. Contrary to studies with other substrates, the pH dependence of the HRP-H–NADH reaction can be interpreted in terms of a single ionization with pKa of 4.2 ± 1.4 at the active site of HRP-II. An apparent reversibility of the HRP-II–NADH reaction was observed. Over the pH range of 4–10 the rate constant for the reaction of HRP-I with NADH varied from 2.6 × 105 to5.6 × 102 M−1 s−1 and of HRP-II with NADH varied from 4.4 × 104 to 4.1 M−1 s−1. These rate constants must be taken into consideration to explain quantitatively the oxidase reaction of horseradish peroxidase with NADH.

scholarly journals pH-sensitivity of the ribosomal peptidyl transfer reaction dependent on the identity of the A-site aminoacyl-tRNA

2010 ◽  
Vol 108 (1) ◽  
pp. 79-84 ◽  
Author(s):  
Magnus Johansson ◽  
Ka-Weng Ieong ◽  
Stefan Trobro ◽  
Peter Strazewski ◽  
Johan Åqvist ◽  
...  
Keyword(s):  
Ph Value ◽  
Ph Dependence ◽  
Peptide Bond ◽  
Bulk Solution ◽  
Peptide Bond Formation ◽  
Transfer Rates ◽  
Peptidyl Transfer ◽  
A Site ◽  
Rate Limiting ◽  
Site Binding

We studied the pH-dependence of ribosome catalyzed peptidyl transfer from fMet-tRNAfMet to the aa-tRNAs Phe-tRNAPhe, Ala-tRNAAla, Gly-tRNAGly, Pro-tRNAPro, Asn-tRNAAsn, and Ile-tRNAIle, selected to cover a large range of intrinsic pKa-values for the α-amino group of their amino acids. The peptidyl transfer rates were different at pH 7.5 and displayed different pH-dependence, quantified as the pH-value, , at which the rate was half maximal. The -values were downshifted relative to the intrinsic pKa-value of aa-tRNAs in bulk solution. Gly-tRNAGly had the smallest downshift, while Ile-tRNAIle and Ala-tRNAAla had the largest downshifts. These downshifts correlate strongly with molecular dynamics (MD) estimates of the downshifts in pKa-values of these aa-tRNAs upon A-site binding. Our data show the chemistry of peptide bond formation to be rate limiting for peptidyl transfer at pH 7.5 in the Gly and Pro cases and indicate rate limiting chemistry for all six aa-tRNAs.

Oxidation of Nickel(II) and Manganese(II) by Peroxodisulfate in Aqueous Solution in the Presence of Molybdate. Crystal Structure of the (NH4)6[NiMo9O32].6H2O Product

1992 ◽  
Vol 45 (12) ◽  
pp. 1943 ◽  
Author(s):  
SJ Dunne ◽  
RC Burns ◽  
GA Lawrance
Keyword(s):  
Rate Constant ◽  
Linear Dependence ◽  
Ph Dependence ◽  
Order Rate Constant ◽  
X Ray Diffraction ◽  
X Ray ◽  
First Order ◽  
Oxidant Concentration ◽  
Ph Range ◽  
Kinetics Of

Oxidation of Ni2+,aq, by S2O82- to nickel(IV) in the presence of molybdate ion, as in the analogous manganese system, involves the formation of the soluble heteropolymolybdate anion [MMogO32]2- (M = Ni, Mn ). The nickel(IV) product crystallized as (NH4)6 [NiMogO32].6H2O from the reaction mixture in the rhombohedra1 space group R3, a 15.922(1), c 12.406(1) � ; the structure was determined by X-ray diffraction methods, and refined to a residual of 0.025 for 1741 independent 'observed' reflections. The kinetics of the oxidation were examined at 80 C over the pH range 3.0-5.2; a linear dependence on [S2O82-] and a non-linear dependence on l/[H+] were observed. The influence of variation of the Ni/Mo ratio between 1:10 and 1:25 on the observed rate constant was very small at pH 4.5, a result supporting the view that the precursor exists as the known [NiMo6O24H6]4- or a close analogue in solution. The pH dependence of the observed rate constant at a fixed oxidant concentration (0.025 mol dm-3) fits dequately to the expression kobs = kH [H+]/(Ka+[H+]) where kH = 0.0013 dm3 mol-1 s-1 and Ka = 4-0x10-5. The first-order dependence on peroxodisulfate subsequently yields a second-order rate constant of 0.042 dm3 mol-1 s-1. Under analogous conditions, oxidation of manganese(II) occurs eightfold more slowly than oxidation of nickel(II), whereas oxidation of manganese(II) by peroxomonosulfuric acid is 16-fold faster than oxidation by peroxodisulfate under similar conditions.

scholarly journals Mitochondrial adenosine triphosphatase from human placenta--inhibition by free magnesium ions of ITP hydrolysis.

1994 ◽  
Vol 41 (1) ◽  
pp. 39-44 ◽  
Author(s):  
Z Aleksandrowicz
Keyword(s):  
Competitive Inhibition ◽  
Competitive Inhibitor ◽  
Hill Coefficient ◽  
Negative Cooperativity ◽  
Magnesium Ions ◽  
Beef Liver ◽  
Bicarbonate Ions ◽  
The Hill ◽  
Kinetics Of ◽  
Free Magnesium

The effects of Mg2+ and bicarbonate on the kinetics of ITP hydrolysis by soluble ATPase (F1) from human placental mitochondria were studied. Increasing amounts of Mg2+ at fixed ITP concentration, caused a marked activation of F1 followed by inhibition at higher Mg2+ concentration. The appropriate substrate for the mitochondrial F1 seems to be the MgITP complex as almost no ITP was hydrolysed in the absence of magnesium. Mg2+ behaved as a competitive inhibitor towards the MgITP complex. In this respect the human placental enzyme differ from that from other sources such as yeast, beef liver or rat liver. The linearity of the plot presenting competitive inhibition by free Mg2+ of MgITP hydrolysis (in the presence of activating bicarbonate anion) suggests that both Mg2+ and MgITP bind to the same catalytic site (Km(MgITP) = 0.46 mM, Ki(Mg) = 4 mM). When bicarbonate was absent in the ITPase assay, placental F1 exhibited apparent negative cooperativity in the presence of 5 mM Mg2+, just as it did with MgATP as a substrate under similar conditions. Bicarbonate ions eliminated the negative cooperativity with respect to ITP (as the Hill coefficient of 0.46 was brought to approx. 1), and thus limited inhibition by free Mg2+. The results presented suggest that the concentration of free magnesium ions may be an important regulatory factor of the human placental F1 activity.

Sign in / Sign up

Export Citation Format

Share Document