X-Chymotrypsin

Fig. 9. Adsorption isotherms where the adsorbed mass f/rngm 2, of various sorbent surfaces is plotted against the protein concentration cl g dm 3, in solution. Sorbents Teflon (o), polystyrene (x),... 

Numerous suggestions have been made that enzymes might owe part of their catalytic efficiency to the opportunity they afford for stabilization of intermediates or transition states by hydrogen bonding to functional groups near the active site. For example, in the case of (x-chymotrypsin this might be represented as in [43] where... 

The proteolytic enzymes, trypsin, chymotrypsin, and chymoral [8076-22-0] in combination, have been used for the treatment of post-operative hand trauma, athletic injuries, and sciatica (214—216). Trypsin has also been used successfully in treating hyaline membrane disease of newborn babies, a condition usually fatal without treatment (217). Immobilized preparations of trypsin are useful in treating acute radiation cystitis following pelvic x-irradiation therapy (218). 

X-ray crystallographic studies of serine protease complexes with transition-state analogs have shown how chymotrypsin stabilizes the tetrahedral oxyanion transition states (structures (c) and (g) in Figure 16.24) of the protease reaction. The amide nitrogens of Ser and Gly form an oxyanion hole in which the substrate carbonyl oxygen is hydrogen-bonded to the amide N-H groups. 

Fig. 4. HPHIC of standard proteins on the weak hydrophobic columns. The SynChro-pack PROPYL column was 25x0.41 cm Poly (alkyl aspartamid)-silicas were packed into 20 x 0.46 cm columns. Sample 25 pi containing 25 pg of each protein in buffer A. Buffer A 1.8 mol/1 ammonium sulphate + 0.1 mol/1 potassium phosphate, pH 7.0. Buffer B 0.1 mol/1 potassium phosphate, pH 7.0. Gradient 40-min linear 0-100% buffer B. Flow rate 1 ml/min. Detection A220 = 1-28 a.u.f.s. Peaks a = cytochrome C, b = ribonu-clease A, c = myoglobin, d = conalbumin, e = neochymotrypsin, / = a-chymotrypsin, g - a-chymotrypsinogen A [48]...

The elucidation of the X-ray structure of chymotrypsin (Ref. 1) and in a later stage of subtilisin (Ref. 2) revealed an active site with three crucial groups (Fig. 7.1)-the active serine, a neighboring histidine, and a buried aspartic acid. These three residues are frequently called the catalytic triad, and are designated here as Aspc Hisc Serc (where c indicates a catalytic residue). The identification of the location of the active-site groups and intense biochemical studies led to several mechanistic proposals for the action of serine proteases (see, for example, Refs. 1 and 2). However, it appears that without some way of translating the structural information to reaction-potential surfaces it is hard to discriminate between different alternative mechanisms. Thus it is instructive to use the procedure introduced in previous chapters and to examine the feasibility of different... 

The successful use of these X-ray crysallographic techniques in studying the enzyme-substrate interactions of lysozyme (21) and chymotrypsin (22) has recently been reviewed by Blow and Steitz (16) and Blow (23). To date, however, these methods have had only limited application, since the detailed structures of only about ten enzymes have been elucidated by X-ray diffraction... 

Figure 6 Separation of basic proteins on an untreated fused silica capillary with diaminopropane as buffer additive. Capillary 75 cm (55 cm to detector) x 50 p i.d. Buffer pHs are as noted on the figure with 30 to 60 mM DAP as an additive 200 to 240 V/cm peak identification 1 = lysozyme, 2 = cytochrome, 3 = ribonuclease, 4 = a-chymotrypsin 5 = trypsinogen, 6 = r-huIL-4. (From Bullock, J. A. and Yuan, L.-C., /. Microcol. Sep., 3, 241, 1991. With permission.)...

Fig. 11. Temperature dependency of the specific activity of a-chymotrypsin in solution (o), adsorbed on silica ( ), Teflon (x), polystyrene (A) and polystyrene —(EO)g ( ). Conditions as in Fig. 9. (Redrawn from Zoungrana and Norde...

Figure 4.21 Monitoring of an enzyme reaction using size-exclusion liquid chromatography. Column, TSK GEL G3000SW, 60 cm x 7.5 mm i.d. eluent, 0.07 M potassium phosphate buffer containing 0.1 M potassium chloride flow rate, 1 ml min-1 detection, UV 280 nm. Peaks 1, fl-lactoglobulin 2, a-chymotrypsin, and 3, decomposed products.

X.-Y. Liu, K. O. Cottrell, and T. M. Nordlund, Spectroscopy and fluorescence quenching of tyrosine in lima bean trypsin/chymotrypsin inhibitor and model peptides, Photochem. 

Kirsh et al. 42) prepared apolar derivatives of poly(4-vinylpyridine) by benzylation. With nitrophenyl acetate as the substrate the benzylated catalyst is 100 times more effective than 4-ethylpyridine. A double-displacement mechanism was observed. The rate constants for deacylation of the acylpoly(vinylpyridine) derivatives were about 4 x 10" /sec. The comparable value for a-chymotrypsin is 8 x 10 /sec. The factor of 20 seems small, but it should be kept in mind that deacetylation of a-chymotrypsin is very slow compared with the deacylation reactions involving the natural substrates of the enzyme. 

From the second-order rate constant for imidazole-catalysed cyclization of the ethyl ester (34) (8 x 10 M s" ) and the rate constant for acylation of a-chy mo trypsin by N-acetyltyrosine ethyl ester (1600 s ), it can be calculated that, in order to attain a rate constant of the magnitude seen in the a-chymotrypsin reaction, a neighbouring imidazole would have to possess an effective molarity of 200,000 M. An effective concentration of this magnitude is not unreasonable, but it is probable that other factors are also important in the enzymatic reaction. 

Table 3.2 Values of (kc /Km)app (M 1 min-1) x 100 for freely suspended and glass-immobilized a-chymotrypsin in various solvents. In all solvent conditions, the enzyme is 1-2 orders of magnitude more active than the free, lyophilized enzyme [78].

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