scholarly journals Catalytic activity of α-chymotrypsin in which histidine-57 has been methylated

1971 ◽  
Vol 124 (1) ◽  
pp. 13-18 ◽  
Author(s):  
R. Henderson
Keyword(s):  
Catalytic Activity ◽  
Normal Function ◽  
Basic Group ◽  
Modified Enzyme ◽  
Chymotrypsin A

The properties of a derivative of α-chymotrypsin in which histidine-57 has been methylated have been examined. Although the modified enzyme binds substrate with the same affinity as does native α-chymotrypsin, acylation and deacylation occur at much decreased rates. As for native α-chymotrypsin, a basic group of pKa approx. 7 is involved in both acylation and deacylation. The significance of these results is considered in relation to the normal function of histidine-57.

The Inhibition of chymotrypsins A4 and B with chloromethyl ketone reagents

1968 ◽  
Vol 46 (11) ◽  
pp. 1357-1370 ◽  
Author(s):  
Kenneth J. Stevenson ◽  
Lawrence B. Smillie
Keyword(s):  
Aromatic Ring ◽  
Histidine Residue ◽  
Straight Chain ◽  
Isolation And Identification ◽  
Chloromethyl Ketone ◽  
Basic Group ◽  
Chymotrypsin B ◽  
Chymotrypsin A

The inactivation of chymotrypsin A4 and B by the bifunctional reagents L-(1-tosylamido-2-phenyl) ethyl chloromethyl ketone (L-TPCK) and phenoxymethyl chloromethyl ketone (PMCK) has been investigated. The rate of inactivation of chymotrypsin A4 with both reagents as a function of pH has been shown to be dependent on a basic group of pK = 6.3–6.5. Chymotrypsin B inactivation appears to be dependent on a basic group with a somewhat lower pK. For each enzyme the reaction with both reagents is associated with the loss of a single histidine residue. By the isolation and identification of 3-carboxymethylhistidine from the alkylated and oxidized peptic histidine-57 peptides, it has been concluded that both enzymes are alkylated at the nitrogen-3 position of histidine-57 by L-TPCK and PMCK. Evidence for the submolar alkylation of methionine-192 of chymotrypsin A4 by L-TPCK, PMCK, D-(1-tosylamido-2-phenyl) ethyl chloromethyl ketone (D-TPCK), and N-methyl-L-TPCK is presented. There is no alkylation of the histidine of chymotrypsin A4 by D-TPCK or.N-methyl-L-TPCK.From a comparison of the structures of a number of reagents known to alkylate chymotrypsin A4, it has been concluded that the alkylation of methionine-192 is nonspecific and relatively independent of any defined stereochemistry of the reagent employed. To date the alkylation of histidine-57 has been shown to occur only with haloketones, and is dependent on the distance between the haloketone and the aromatic ring when the latter is present. Although the presence of an asymmetric α-carbon and acylamido group in straight-chain reagents is unnecessary for histidine alkylation, these must be of the L configuration if present.

The inhibition of chymotrypsin A4 with a homologous series of chloromethyl ketone reagents

1970 ◽  
Vol 48 (3) ◽  
pp. 364-375 ◽  
Author(s):  
Kenneth J. Stevenson ◽  
Lawrence B. Smillie
Keyword(s):  
Binding Site ◽  
Homologous Series ◽  
Imidazole Ring ◽  
The Other ◽  
Chloromethyl Ketone ◽  
Basic Group ◽  
Acid Hydrolysate ◽  
Other Hand ◽  
Hydrophobic Binding ◽  
Chymotrypsin A

The inactivation of chymotrypsin A4 (CHT-A4) by a homologous phenylalkyl series of bifunctional reagents, viz. phenyl chloromethyl ketone (PCK), benzyl chloromethyl ketone (BCK), and β-phenylethyl chloromethyl ketone (βPECK) (C6H5 [CH2]n COCH2Cl where n = 0, 1, or 2), has been investigated. The inactivation of CHT-A4 by PCK has been shown to be essentially pH independent whereas inactivation by BCK and βPECK appears to be dependent on a basic group of pK 6.0–6.3. PCK has been shown to inhibit CHT-A4 by virtue of the complete S-alkylation of methionine-192. BCK and βPECK, on the other hand, inactivate CHT-A4 through a combination of partial S-alkylation of methionine-192 (0.2 and 0.3 residue, respectively) and partial alkylation of histidine-57 (0.2 and 0.4 residue, respectively). Identification of the particular residue alkylated was obtained through the isolation and analysis of alkylated and oxidized peptic peptides obtained from the alkylated CHT-A4 by the diagonal peptide ionophoresis technique.The initial site of alkylation of BCK and βPECK on the imidazole ring of histidine-57 has not been identified. However, a unique histidine derivative has been isolated from the acid hydrolysate of oxidized histidine-57 peptide from CHT-A4–βPECK and is suggested to be 2(or 4)-hydroxymethylhistidine.On the basis of the present studies on the phenylalkyl series and on studies reported earlier on a phenylalkylamido halomethyl ketone series of bifunctional reagents which alkylates only methionine in CHT-A4, it has been suggested that alkylation of histidine by members of the phenylalkyl series is primarily a result of binding to the hydrophobic binding site of CHT-A4 rather than binding to the acylamido binding site as is suggested to be the case for the phenylalkylamido series.

scholarly journals A Kinetic Approach to Defining the Role of Chemically Modifiable Residues at the Active Sites of Enzymes

1975 ◽  
Vol 28 (4) ◽  
pp. 379
Author(s):  
Leonie K Ashman ◽  
D Bruce Keech
Keyword(s):  
Biological Activity ◽  
Catalytic Activity ◽  
Kinetic Analysis ◽  
Active Site ◽  
Initial Velocity ◽  
Active Sites ◽  
Kinetic Approach ◽  
Modified Enzyme ◽  
Enzyme Molecules

Initial velocity studies can be used to define the function of chemically modifiable residues in the active site of a multisubstrate enzyme. Since the method relies on measuring biological activity, it has the advantage that it can be used with small amounts of relatively impure enzyme, but requires that modified enzyme molecules have some residual catalytic activity. The kinetic analysis of the modified enzyme can be carried out in the presence of some unmodified enzyme molecules.

High resolution electron microscopy of lanthanum phosphate crystals

1978 ◽  
Vol 36 (1) ◽  
pp. 274-275
Author(s):  
J. C. Wheatley ◽  
J. M. Cowley
Keyword(s):  
Electron Microscopy ◽  
Catalytic Activity ◽  
High Resolution ◽  
Petroleum Industry ◽  
High Resolution Electron Microscopy ◽  
Lanthanum Phosphate ◽  
Good Catalyst ◽  
Resolution Electron ◽  
Good Catalytic Activity ◽  
Physical And Chemical

Rare-earth phosphates are of particular interest because of their catalytic properties associated with the hydrolysis of many aromatic chlorides in the petroleum industry. Lanthanum phosphates (LaPO4) which have been doped with small amounts of copper have shown increased catalytic activity (1). However the physical and chemical characteristics of the samples leading to good catalytic activity are not known.Many catalysts are amorphous and thus do not easily lend themselves to methods of investigation which would include electron microscopy. However, the LaPO4, crystals are quite suitable samples for high resolution techniques.The samples used were obtained from William L. Kehl of Gulf Research and Development Company. The electron microscopy was carried out on a JEOL JEM-100B which had been modified for high resolution microscopy (2). Standard high resolution techniques were employed. Three different sample types were observed: 669A-1-5-7 (poor catalyst), H-L-2 (good catalyst) and 27-011 (good catalyst).

The design and catalytic performance of molybdenum active sites on an MCM-41 framework for the aerobic oxidation of 5-hydroxymethylfurfural to 2,5-diformylfuran

2019 ◽  
Vol 9 (3) ◽  
pp. 811-821 ◽  
Author(s):  
Zhao-Meng Wang ◽  
Li-Juan Liu ◽  
Bo Xiang ◽  
Yue Wang ◽  
Ya-Jing Lyu ◽  
...  
Keyword(s):  
Catalytic Activity ◽  
Active Sites ◽  
Aerobic Oxidation ◽  
Catalytic Performance ◽  
Mcm 41

The catalytic activity decreases as –(SiO)3Mo(OH)(O) > –(SiO)2Mo(O)2 > –(O)4–MoO.

Metallic prions

2004 ◽  
Vol 71 ◽  
pp. 193-202 ◽  
Author(s):  
David R Brown
Keyword(s):  
Prion Protein ◽  
Binding Capacity ◽  
Normal Function ◽  
Transmissible Spongiform Encephalopathies ◽  
Published Data ◽  
Normal Brain ◽  
Copper Binding ◽  
Loss Of Function ◽  
Spongiform Encephalopathies ◽  
The Brain

Prion diseases, also referred to as transmissible spongiform encephalopathies, are characterized by the deposition of an abnormal isoform of the prion protein in the brain. However, this aggregated, fibrillar, amyloid protein, termed PrPSc, is an altered conformer of a normal brain glycoprotein, PrPc. Understanding the nature of the normal cellular isoform of the prion protein is considered essential to understanding the conversion process that generates PrPSc. To this end much work has focused on elucidation of the normal function and activity of PrPc. Substantial evidence supports the notion that PrPc is a copper-binding protein. In conversion to the abnormal isoform, this Cu-binding activity is lost. Instead, there are some suggestions that the protein might bind other metals such as Mn or Zn. PrPc functions currently under investigation include the possibility that the protein is involved in signal transduction, cell adhesion, Cu transport and resistance to oxidative stress. Of these possibilities, only a role in Cu transport and its action as an antioxidant take into consideration PrPc's Cu-binding capacity. There are also more published data supporting these two functions. There is strong evidence that during the course of prion disease, there is a loss of function of the prion protein. This manifests as a change in metal balance in the brain and other organs and substantial oxidative damage throughout the brain. Thus prions and metals have become tightly linked in the quest to understand the nature of transmissible spongiform encephalopathies.

Minerals Intake Distributions in a Large Sample of Iranian at-Risk Population Using the National Cancer Institute Method: Do They Meet Their Requirements?

2015 ◽  
Vol 85 (3-4) ◽  
pp. 129-144 ◽  
Author(s):  
Zahra Heidari ◽  
Awat Feizi ◽  
Leila Azadbakht ◽  
Nizal Sarrafzadegan
Keyword(s):  
At Risk ◽  
National Cancer Institute ◽  
Population Based ◽  
Cross Sectional Study ◽  
Normal Function ◽  
Dietary Intakes ◽  
Middle Aged ◽  
Cross Sectional ◽  
Nutritional Interventions ◽  
High Prevalence

Abstract. Background: Minerals are required for the body’s normal function. Aim: The current study assessed the intake distribution of minerals and estimated the prevalence of inadequacy and excess among a representative sample of healthy middle aged and elderly Iranian people. Methods: In this cross-sectional study, the second follow up to the Isfahan Cohort Study (ICS), 1922 generally healthy people aged 40 and older were investigated. Dietary intakes were collected using 24 hour recalls and two or more consecutive food records. Distribution of minerals intake was estimated using traditional (averaging dietary intake days) and National Cancer Institute (NCI) methods, and the results obtained from the two methods, were compared. The prevalence of minerals intake inadequacy or excess was estimated using the estimated average requirement (EAR) cut-point method, the probability approach and the tolerable upper intake levels (UL). Results: There were remarkable differences between values obtained using traditional and NCI methods, particularly in the lower and upper percentiles of the estimated intake distributions. A high prevalence of inadequacy of magnesium (50 - 100 %), calcium (21 - 93 %) and zinc (30 - 55 % for males > 50 years) was observed. Significant gender differences were found regarding inadequate intakes of calcium (21 - 76 % for males vs. 45 - 93 % for females), magnesium (92 % vs. 100 %), iron (0 vs. 15 % for age group 40 - 50 years) and zinc (29 - 55 % vs. 0 %) (all; p < 0.05). Conclusion: Severely imbalanced intakes of magnesium, calcium and zinc were observed among the middle-aged and elderly Iranian population. Nutritional interventions and population-based education to improve healthy diets among the studied population at risk are needed.

Achilles Tenorrhaphy in Five Dogs: A Modified Surgical Technique and Evaluation of a Cranial Half Cast

1998 ◽  
Vol 11 (04) ◽  
pp. 205-210 ◽  
Author(s):  
H. Burbidge ◽  
E. Firth ◽  
S. Fox ◽  
S. Guerin
Keyword(s):  
Soft Tissue ◽  
Surgical Technique ◽  
Surgical Procedure ◽  
Normal Function ◽  
Surgical Reconstruction ◽  
Bone Apposition ◽  
Cast Material ◽  
Bilateral Lesions ◽  
Bone Tunnels

SummaryAchilles mechanism rupture in four of five dogs was treated with tenorrhaphy using a modified surgical technique designed to optimise accurate apposition of tendon to bone. Two bone tunnels were drilled in the calcaneal tuber from a plantomedial - dorsolateral, and plantolateral – dorsomedial direction respectively. The distal ends of the tendons were sutured to the calcaneal tuber using a Krachow suture pattern. The remaining dog had a mid-tendon Achilles mechanism rupture. A resinous half cast was placed on the cranial aspect of the tarsocrural joint of all five dogs, for a minimum of six weeks, in order to provide limited post operative support. Du e to insufficient cast material two of the support splints failed and one of these cases also required a second surgical procedure. A varying amount of soft tissue irritation was noted in each case. All of the five Achilles mechanisms healed, and all of the dogs returned to normal function.Five dogs with surgical reconstruction of the Achilles mechanism were stabilised postoperatively with a resinous half cast placed on the cranial aspect of the tarsocrural joint for a minimum of six weeks. Two of these casts failed at the tarsocrural joint when six folds of casting material were used; all subsequent cases had eight folds applied. Variable soft tissue irration was observed under the cast in each case. A modified surgical technique using a Krachow suture pattern allowed good tendon-bone apposition. All five Achilles mechanisms healed, and all dogs returned to normal function. Bilateral lesions were identified in 3 of the 4 dogs examined.

Prolonged Expression of Procoagulant Activity of Human Platelets Degranulated by Thrombin

1995 ◽  
Vol 74 (03) ◽  
pp. 958-961 ◽  
Author(s):  
Raelene L Kinlough-Rathbone ◽  
Dennis W Perry
Keyword(s):  
Catalytic Activity ◽  
Thrombus Formation ◽  
Annexin V ◽  
Human Platelets ◽  
Procoagulant Activity ◽  
Prothrombinase Complex ◽  
Arterial Thrombus ◽  
Flowing Blood

SummaryPlatelets are exposed to thrombin when they take part in arterial thrombus formation, and they may return to the circulation when they are freed by fibrinolysis and dislodged by flowing blood. Thrombin causes the expression of procoagulant activity on platelets, and if this activity persists, the recirculating platelets may contribute to subsequent thrombosis. We have developed techniques to degranulate human platelets by treatment with thrombin, and recover them as single, discrete platelets that aggregate in response to both weak and strong agonists. In the present study we examined the duration of procoagulant activity on the surface of thrombin-degranulated platelets by two methods: a prothrombinase assay, and the binding of 125I-labeled annexin. Control platelets generated 0.9 ± 0.4 U thrombin per 107 platelets in 15 min. Suspensions of thrombin-degranulated platelets formed 5.4 ± 0.1 U thrombin per 107 platelets in this time. Binding of 125I-annexin V was also greater with thrombin-treated platelets than with control platelets (controls: 1.7 ±0.1 ng annexin/107 platelets; thrombin-degranulated platelets: 6.8 ± 0.2 ng annexin/107 platelets). With thrombin-degranulated platelets, increased procoagulant activity and annexin binding persisted for at least 4 h after degranulation and resuspension, indicating that the catalytic activity for the prothrombinase complex is not reversed during this time. These platelets maintained their ability to aggregate for 4 h, even in response to the weak agonist, ADP. Thus, platelets that have taken part in thrombus formation and returned to the circulation may contribute to the promotion of further thrombotic events because of the persistence of procoagulant activity on their surface.

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