Enzyme crystalline

Fig. 1. Taxon specificity in crystallin expression, as revealed by SDS-PAGE analysis of lens extracts from mammals (A) and birds (B). Major enzyme crystallins are indicated. In (B) the variability in / 1 (fl) mobility among birds is apparent. [For full species names, see G. Wistow, E. Roquemore, and H. S. Kim, Curr. Eye Res. 10, 313 (1991), and G. Wistow and H. Kim, J. Mol. Evol. 32,262 (1991), from which this figure is adapted.] (A) M, Marker Wb, wallaby Es, elephant shrew Rb, rabbit Mo, mouse Cv, rock cavy. (B) M, Marker Am, merganser Bd, black duck Sf, chimney swift Hb, hummingbird St, starling Sw, bam swallow Rh, rhea Sp, house sparrow Rc, raccoon (a mammal for comparison).

Starch is hydrolyzed or broken down into its constituent sugars by enzymes. Crystalline raw starch cannot be digested very well. Eating grains before fire was available for cooking was not a very useful way to get energy. Pure starch is a white, tasteless and odorless powder that is insoluble... 

Enzymes are obtained from plants, animals and micro-organisms by extraction with a suitable solvent, preferably after the cell structure has been destroyed by drying or grinding. They can be purified by precipitation and resolution and by fractional absorption and elution. Many enzymes have been obtained crystalline. 

Urease is one of the enzymes which have been obtained in the crystalline state. This has been done by stirring jack bean meal with 30°o aqueous acetone, filtering and allowing the filtrate to remain at o for several hours. The urease which crystallises out is separated by centrifuging and is then recrystallised. Like crystalline pepsin and trypsin, it is a protein. 

An important chemical finishing process for cotton fabrics is that of mercerization, which improves strength, luster, and dye receptivity. Mercerization iavolves brief exposure of the fabric under tension to concentrated (20—25 wt %) NaOH solution (14). In this treatment, the cotton fibers become more circular ia cross-section and smoother ia surface appearance, which iacreases their luster. At the molecular level, mercerization causes a decrease ia the degree of crystallinity and a transformation of the cellulose crystal form. These fine stmctural changes iacrease the moisture and dye absorption properties of the fiber. Biopolishing is a relatively new treatment of cotton fabrics, involving ceUulase enzymes, to produce special surface effects (15). 

D-Glucose is produced by complete depolymerization of starch with enzymes that catalyze the hydrolysis of both its (1 — 4) and (1 — 6) linkages. Crystalline a-D-glucopyranose is generally sold as dextrose. Glucose is also isomerized to D-fmctose to produce high fmctose com symp (HFCS). 

Purification. Enzyme purity, expressed in terms of the percent active enzyme protein of total protein, is primarily achieved by the strain selection and fermentation method. In some cases, however, removal of nonactive protein by purification is necessary. The key purification method is selective precipitation of the product or impurities by addition of salt, eg, sodium sulfate, or solvent, eg, ethanol or acetone by heat denaturation or by isoelectric precipitation, ie, pH adjustments. Methods have been introduced to produce crystalline enzyme preparations (24). 

Most of the known antiparallel p structures, including the immunoglobulins and a number of different enzymes, have barrels that comprise at least one Greek key motif. An example is 7 crystallin, which has two consecutive Greek key motifs in each of two barrel domains. These four motifs are homologous in terms of both their three-dimensional structure and amino acid sequence and are thus evolutionarily related. 

Smith, S.O., et al. Crystal versus solution structures of enzymes NMR spectroscopy of a crystalline serine protease. Science 244 961-964, 1989. 

Stibine, see Antimony hydride Stoddard solvent Strontium chromate Strychnine Styrene, monomer Subtilisins (proteolitic enzymes as 100% pure crystalline enzyme)... 

At best, van der Waals interactions are weak and individually contribute 0.4 to 4.0 kj/mol of stabilization energy. ITowever, the sum of many such interactions within a macromolecule or between macromolecules can be substantial. For example, model studies of heats of sublimation show that each methylene group in a crystalline hydrocarbon accounts for 8 k[, and each C—IT group in a benzene crystal contributes 7 k[ of van der Waals energy per mole. Calculations indicate that the attractive van der Waals energy between the enzyme lysozyme and a sugar substrate that it binds is about 60 k[/mol. 

Until the discovery in 1975 of nickel in jack bean urease (which, 50 years previously, had been the first enzyme to be isolated in crystalline form and was thought to be metal-free) no biological role for nickel was known. Ureases occur in a wide variety of bacteria and plants, catalyzing the hydrolysis of urea,... 

The reaction was catalyzed by a partially purified enzyme preparation from a mutant of Bacillus pumillus (see the next subsection). From 1 g of D-glyceralde-hyde and 1 g of acetoin, 0.67 g of pure crystalline 1 -deoxy-D-r/treo-pentulose was obtained in one operation. The sugar was fully characterized. 

His work on enzymes was continued during the Bonn period. Studies on acid phosphatases were carried out that made a major contribution to our knowledge of these enzymes. " The isolation of a crystalline /3-glucosidase from the emulsin of sweet almonds may be regarded as the crowning achievement of his work on glycosidases. ... 

---