Beans, jack

Ltease test. The enzyme uretwe hydrolyses urea to ammonium carbonate (p. 519). The reaction is sp ific and is frequently used for solu tions of urea to which the biuret test cannot be applied. Add about 5 drops of phenohred to o 2 g. of urea dissolved in 5 ml. of water. To this yellow solution, add 0 2 g. of jack bean meal suspended in 2 ml. of water containing. also 5 drops of phenol-red. The colour changes to red as the solution becomes alkaline. 

Urease soya bean, jack bean urea ammonium carbonate 7-2-7 9... 

The chief sources of this important enzyme are (a) the jack bean (Canavalia ensiformis). (b) the soy (or soja) bean (Glycine hispida). The enzyme is of great value in identifying and estimating urea. The action of urease on urea is specific, the reaction catalysed being ... 

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. 

Place about 0 2 g. of jack-bean meal in a test-tube, add 2 ml. of water and about 5 drops of phenol-red. Mix thoroughly and allow the faintly yellow solution to stand while the urea solution is being made up. 

Urease solution. Place about 5 g. of jack-bean meal in a mortar and grind up with about 10 ml. of water, t hen add about 90 ml. of water, mix thoroughly and allow to stand for some time in order to deposit starch and other insoluble substances. Decant off the supernatant liquid into a conical flask and cork the latter. 

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,... 

Concanavalin A is a plant lectin from the jack bean (Canavalia ensiformis) which binds with high affinity to mannose residues of glycoproteins. Concanavalin A is known to stimulate the tyrosine kinase activity of the INSR (3-subunit with consecutive activation of kinases downstream the insulin receptor (IRS, PI 3-kinase). It is believed that Concanavalin A stimulates the activation and autophosphorylation of the INSR kinase through aggregation of the receptor, although the precise mechanism of action is unclear. 

A case similar to the slow, practically irreversible inhibition of jack bean a-D-mannosidase by swainsonine is represented by the interaction of castanospermine with isomaltase and rat-intestinal sucrase. Whereas the association constants for the formation of the enzyme-inhibitor complex were similar to those of other slow-binding glycosidase inhibitors (6.5 10 and 0.3 10 M s for sucrase and isomaltase, respectively), the dissociation constant of the enzyme-inhibitor complex was extremely low (3.6 10 s for sucrase) or could not be measured at all (isomaltase), resulting in a virtually irreversible inhibition. Danzin and Ehrhard discussed the strong binding of castanospermine in terms of the similarity of the protonated inhibitor to a D-glucosyl oxocarbenium ion transition-state, but were unable to give an explanation for the extremely slow dissociation of the enzyme-inhibitor complex. 

Group (c), a-D-mannosidase from jack beans and from almonds, and a-D-galactosidase from coffee beans, showed no inactivation. The results with these enzymes can possibly be explained by the formation of a (weak) non-covalent complex in which glycosylation is too slow to cause inactivation within the time period of measurements, or, less likely, rapid hydrolysis of the glycosyl-enzyme intermediate. 

Fig. 4. Backscattered Raman and ROA spectra of the n-helical protein human serum albumin in H20 (top pair) and the /3-sheet protein jack bean concanavalin A in acetate buffer solution at pH 5.4, together with MOLSCRIPT diagrams (Kraulis, 1991) of their X-ray crystal structures (PDB codes lao6 and 2cna). 

According to the PDB X-ray crystal structure 2cna, jack bean con-canavalin A contains 43.5% /1-strand, 1.7% a-helix, and 1.3% 3io-helix,... 

The backbone skeletal stretch region is rather ambiguous for /1-sheet assignments. As may be seen in the ROA spectrum of jack bean con-canavalin A (Fig. 4), there are many bands in this region, mostly positive. These bands can be rather variable in intensity, width, and wavenumber in /3-sheet proteins, which may reflect the various types of distortions found in /3-sheet. 

Proteins containing a large amount of antiparallel /3-sheet usually show negative ROA bands in the range 1340—1380 cm-1, especially if the /3-sheet is extended as in a sandwich or barrel, which appear to originate in tight turns of the type found in /3-hairpins. One example is the band at 1345 cm-1 in jack bean concanavalin A (Fig. 4). These bands do not appear in the ROA spectra of a/// proteins, since these contain only parallel /6-sheet with the ends of the parallel /6-strands connected by a-helical sequences rather than tight turns (Barron etal., 2000). 

Laufberger had tried to obtain the protein from horse liver, but it did not crystallize, and as he described to me when I met him in Prague some years ago, in those days everyone wanted to have protein crystals as a criteria of purity. Although James Sumner had crystallized jack bean urease in 1926, his preparations were somewhat impure, and it was only in the mid-1930s, when John Northrop and Moses Kubnitz showed that there is a direct correlation between the enzymatic activities of crystalline pepsin, trypsin and chymotrypsin that the protein nature of enzymes was generally accepted. 

Jack-bean aldolase and liver aldolase catalyze the conversion of one mole of D-fructose 1-phosphate into one mole each of dihydroxyacetone phosphate and D-glycerose, and the reaction is reversible.73-77... 

Con A Jack bean seeds a-D-Mannose, a-D-glucose a-D-Methyl mannose... 

Historically the earliest Ni-containing enzyme to be described was urease from jack bean meal, which was crystallized by James Sumner in 19261. However, analytical techniques did not allow urease to be recognized as a Ni-containing enzyme until 50 years later. Urease catalyses the hydrolysis of urea to ammonia and carbamate, which spontaneously hydrolyses to give carbonic acid and a second molecule of ammonia. 

The enzyme urease was discovered in soybeans by Takeuchi in 1909 it catalyzed the conversion of urea to ammonium carbonate. Jack beans were another excellent source of the enzyme. Jack bean powder could be stored for considerable periods and very active, soluble, urease extracted. After the action of urease, the ammonia could be estimated colorimetrically by Nesslerisation or titrimetrically. The Conway diffusion apparatus was specially developed for the estimation of urea titrimetrically and remained in use into the 1950s. 

The protein nature of enzymes was established through the seminal work of James Sumner. In 1926, Sumner succeeded in isolating the enzyme urease in crystalline form from jack bean meal. This was the first time in history that an enzyme had been obtained in crystalline, though not completely pure, form. Subsequently, Sumner established that the crystalline enzyme was a protein. Urease is an enzyme that degrades one of the human end products of nitrogen metabolism, urea, to ammonia and carbon dioxide ... 

Effect of Inhibitors on Arrhenius Plots. The presence of inhibitors can lead to nonlinear Arrhenius plots as well as an increase in E. For example, jack bean urease exhibits a linear Arrhenius plot in the absence of an inhibitor, but a curved plot in the presence of 34 mM sodium sulfite . 

Urease (jack bean) Hypothesized to convert hydroxyurea to HA 57... 

Fig. 23. Methyl a-septanoside mono-, di-, and tri-saccharides 243-245 assayed against jack-bean a-mannosidase.

In the mannosidase series, two GH 38 enzymes, that of jack bean and also almond a-mannosidase, were evaluated with deoxy derivatives of 4-nitrophenyl a-D-manno-pyranoside.126 For both enzymes, it was found that scarcely any hydrolysis took place with the 2-deoxy, 3-deoxy, or 4-deoxy sugars, but the 6-deoxymannopyranoside was turned over at about the same rate as the parent compound, indicating that a strict conservation of functional groups is necessary for productive enzymatic action. 

B. stearothermophilus), (3-galactosidases (bovine liver, S. fragilis, A. oryzae), and jack-bean a-mannosidase 230... 

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