Similarly, hypoxanthine (HX) can be used to label purine residues. As in Problem 4, write reactions showing the conversion of hypox- anthine to DATP and dGTP.
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- The trypsin enzyme is able to hydrolyze a peptide substate at the carboxyl side of an Arg or Lys residue. However, such a reaction can be also influenced by the amino acid residue that follows Arg or Lys. Given the Michaelis-Menton plots obtained for two substrates (substrate A: Ser-Val- Arg-Pro; substrate B: Ser-Val-Arg-Phe), the Km of the enzyme is higher for: 20 Substrate A Assume that these curves do not reach the same limit. 15 Substrate E 0.001 0.002 0.003 (Substrate) (molar) Inconclusive Substrate B Both Substrate A and B Intitial velocity (micromoles/literisecond)The objective is to study a novel protease P isolated from the digestive tract of an Amazonian insect. This protease can exist into two forms Pi and Pa which have identical amino acid sequences (both of 80 kDa). However, only Pa shows proteolytic activity. To better understand the activation mode of Pi (inactive form) in Pa (active form), the following experiment was done using DIPF. DIPF (diisopropylphosphofluoridate) is a well-known irreversible inhibitor of serine proteases. It reacts with the catalytic serine residue of the active site of proteases as shown below: Enzyme -CH₂OH + CH(CH3)2 O F-P=0 O CH(CH3)2 Diisopropylphospho- fluoridate (DIPF) Enzyme -CH,—O CH(CH3)2 O <=0 O CH(CH3)2 DIP-Enzyme Both proteases Pa and P₁ were incubated with 32P-DIPF for 30 min at 37°C, and then dialysed to remove excess of unreacted radiolabelled reagent. The two proteases were then analyzed in Sodium Dodecyl Sulphate-Polyacrylamide Gel Electrophoresis (SDS-PAGE), with and without 2-mercaptoethanol.…When hyaluronan synthase from Pasteurella multocida was expressed in E. coli, the bacteria spun out a capsule of hyaluronan. This reaction was analyzed using purified membrane fragments containing the hyaluronan synthase, a radio-labeled tetrasaccharide acceptor (Part A), along with the activated forms of the sugar subunits: UDP-N-acetylglucosamine and UDP-glucuronic acid. In short incubations with the complete mixture, the tetrasaccharide primer elongated by several units, although only odd-numbered chains were visible (Part B lane 2). If one or both activated sugars were left out, the results shown in lanes 3-5 (Part B) were obtained. Why do you suppose that only odd-number chains are visible in your assay? (A) ACCEPTOR nonreducing end HO- HO OH COO glucuronic acid (GICUA) HO- CH3 T C=O I NH CH₂ OH N-acetylglucosamine (GlcNAc) COO но- HO OH OH I CH₂ reducing end NH C=O CH3 Choose one: O A. Synthase adds GlcNAc much more slowly than it adds GICUA. O B. One of the monosaccharide…
- Diisopropylphosphofluoridate (DIPF) inactivates chymotrypsin by covalently modifying serine 195. Which statement is true of DIPF's inhibitory mechanism? DIPF randomly modifies all serine residues on the protein, and if enough is added, the serine in the active site will eventually be modified. DIPF approaches serine 195 more closely than other substrates. DIPF looks like the substrate for chymotrypsin and binds in the active site as a competitive inhibitor. Serine 195 is in an environment that gives it a higher than normal reactivity with respect to DIPF.Discuss the Pharmacokinetics of morphine sulfate using the correct sequence you have chosen in question number one.Substrate A has a Km of 45uM and a kcat of 100/s with trypsin and a Km of 540mM and a kcat of 2/s with chymotrypsin. Substrate A is a better substrate of [trypsin/chymotrypsin] and likely contains a/an/some [aromatic/acidic/basic] residues(s) in its sequence. Chymotrypsin contains a [glycine/serine/aspartate] in its specificity pocket which likely [repel/attract] the residues in substrate A.
- Thiopurine S-methyltransferase (TPMT) is an enzyme that is responsible for the metabolism of the drugs azathioprine and 6-mercaptopurine, which are used to treat acute lymphoblastic leukemia and inflammatory bowel disease. Metabolism by TPMT reduces the bioavailability of the drugs. In addition to the thiopurine substrates, TPMT also binds S-adenosyl methionine as a cofactor. TPMT is a highly polymorphic enzyme; almost 30 variants are known to be expressed in humans, with most of the variants possessing lower enzymatic activity than the wild-type protein (TPMTwt). Despite having substitutions remote from the active site, TPMT*2 (an A80P variant) and TPMT*5 (an L49S variant) have enzyme activities of 47% and 14% relative to TPMTwt at 18°C, respectively. Two techniques were used to understand the relationships between enzymatic activity and protein stability. Circular dichroism (CD) spectroscopy measures the differential absorption of left and right-circularly polarized light and is used…Some of the following four amino acids : alanine, arginine, histidine, aspartic acid would provide a side chain for acid-base catalysis at physiological pH (assume pK of each amino acid is equal to pK value for the free amino acid in solution). Explain for each amino acid how and why each would or would not provide the side chain residue to support acid-base catalysis at physiological pH.In addition to the reactions mentioned in Section 23.5, PLP can catalyze b-substitution reactions. Propose a mechanism for the following PLP-catalyzedb-substitution reaction:
- Escherichia coli Fpg protein is responsible for removing damaged DNA base pairs such as C8-oxoguanine (8-oxoG). The catalytic mechanism is believed to involve the formation of a transient Schiff base intermediate formed between DNA base the N-terminal proline residue. Draw the structure of PTH-derivative that is formed after Fpg is subjected to one cycle of Edman degradation.Crystal structures exist for three neurokinin-1 (NK1) ligand complexes with the following pdb codes (6hll, 6hlo,6hlp). State which is the highest quality crystal structure indicating the criteria you used to evaluate this.The octapeptide gly-cys-met-asn-lys-ala-tyr-gly was hydrolyzed consecutively by CNBr and then trypsin (3 fragments total). The mixture of fragments was buffered at a pH 8.5 and then chromatographed on an anion-exchanger (positive resin) with the same buffer. Draw sequence (abbreviated form) of all fragments at that pH (show charges) and predict elution order.