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Potassium react with proteins

Prussian Blue is probably the most famous blue pigment. It was discovered by accident in 1704 and is made from potassium ferro-cyanide and ferric chloride. Heinrich Diesbach, a colour manufacturer of Berlin, had run out of potash (potassium carbonate) with which to make a red lake so he borrowed some from Johann Dippel an alchemist. While this worked fine, something happened to the solution after he had filtered off the red lake it turned a deep blue colour. Dip-pel s potash had been made from calcined bones and these contained cyanide from the decomposition of their protein component and the cyanide had reacted to a deep blue compound which we now know as... [Pg.185]

Generally, sodium and potassium react only to a limited extent with proteins, whereas calcium and magnesium are somewhat more reactive. Transition metals, e.g., ions of Cu, Fe, Hg, and Ag, react readily with proteins, many forming stable complexes with thiol groups. Calcium cations and ferrous, cupric, and magnesium cations may be integral parts of certain protein molecules or molecular associations. Their removal by dialysis or sequestration appreciably lowers the stability of the protein structure toward heat and proteases. [Pg.68]

III. The Ordinary Alkaloidal Reagents,—The reagents which precipitate alkaloids from their solutions react also with proteins. Among these may be mentioned phosphotungstic acid, phosphomolybdic acid, tannic acid, picric acid, potassium mercuric iodide, and potassium bismuth iodide. The alkaloidal reagents precipitate the majority of the proteins in acid solution only. [Pg.597]

Figure 3. Oscilloscope trace of a temperature-jump experiment on Octopus hemocyanin reacting with oxygen. Potassium phosphate buffer, 0.2M, pH 7, and 20 C (before the jump). Discharge 30 kv yielding a temperature increase of 4 to 5 C. Protein concentration = 4.5 X 10 binding equivalent L fractional saturation with oxygen = 0.53 free oxygen concentration = 3.4 X lOr M. Sweep time = 100 fxsec per large screen division observation wavelength = 348 nm (24). Figure 3. Oscilloscope trace of a temperature-jump experiment on Octopus hemocyanin reacting with oxygen. Potassium phosphate buffer, 0.2M, pH 7, and 20 C (before the jump). Discharge 30 kv yielding a temperature increase of 4 to 5 C. Protein concentration = 4.5 X 10 binding equivalent L fractional saturation with oxygen = 0.53 free oxygen concentration = 3.4 X lOr M. Sweep time = 100 fxsec per large screen division observation wavelength = 348 nm (24).
When the sarcoplasmic calcium transport system operates in the reverse mode and synthesizes ATP from ADP and inorganic phosphate during calcium release, inorganic phosphate reacts with the transport protein also leading to the formation of a phosphoprotein [115 -117]. This reaction also requires ionized magnesium but is suppressed when the concentration of ionized calcium in the medium exceeds 10 /xM. In the transport protein of the sodium-potassium system, analogous cation dependent phosphoryl transfer reactions take place. It is difficult, however, to directly correlate phosphorylation and ion movement in these membranes. [Pg.198]

The biuret method is based on the fact that proteins (and, as a rule, all substances containing two or more peptidic bonds) react with copper to form a colored complex whose absorption (2max = 454 nm), in the presence of excess copper, is proportional to the amount of protein present. The reagent is obtained by dissolving 1-5 g of copper(II) sulfate and 6g of sodium potassium tartrate tetrahydrate in 3% sodium hydroxide. Bovine serum albumin is used as standard. The most serious drawback of this method is its poor sensitivity. [Pg.4512]

In addition to reacting with enzymes, as described below, both 3 -and 5 -FSBA have been observed to react with certain commonly used buffers, with the concomitant release of fluoride ion in accordance with first-order kinetics. In the case of 3 -FSBA in buffers at pH 8 and 25°, the half-life is about 37 min for 0.01 M potassium phosphate and 0.01 M Tris acetate, whereas triethanolamine chloride at the same pH reacted more vigorously. In 0.01 M sodium barbital at pH 8, the half-life for 3 -FSBA was about 63 min this buffer has proved to be satisfactory for reaction with proteins. The 5 -FSBA does not react as readily with buffers, and at 30° in 0.01 M sodium barbital at pH 7.6, containing 0.2 M KCl and 15% dimethylformamide, its half-life was found to be about 8.4 hr. The reaction with the 3 - and 5 -FSBA might be expected to involve the unprotonated form of susceptible amino acids, and therefore the rate of reaction in many cases may proceed more rapidly at pH values that are on the alkaline side of neutrality. However, it must be kept in mind that the ester linkage of both 3 - and 5 -FSBA has limited stability below pH 6 and above pH 9. [Pg.245]

Larson and Jenness (89,90) have adapted the apparatus used for the dead stop titration (40,130) to the amperometric determination of —SH groups with o-iodosobenzoic acid. The —SH groups are oxidized by o-iodosobenzoate at pH 7 a mixture of acidified potassium iodide and sodium thiosulfate is then added. o-Iodosobenzoate is added to the first appearance of free iodine as determined amperometrically. Iodine can be used directly but this reagent might oxidize —SH groups beyond the —SS— stage and might react with tyrosine and tryptophane residues. The procedure of Larson and Jenness may be of particular value in the analysis of turbid suspensions such as milk or in the presence of denatured proteins. With such suspensions evaluation of the end point with starch in conventional titrations with sodium thiosulfate is difficult. [Pg.19]

Further evidence for the importance of imine formation for T cell function was derived from the discovery that tucaresol and other small molecules with an aromatic aldehyde moiety capable of forming Schiff bases, produces a signal to CD4+ T helper (Th) cells [62]. Tucaresol reacts in vitro with free CD4+ T cell surface amines from receptors like CD2 within seconds to cause a co-stimulatory signal to produce a Thl response with the release of interferon y (IFN-y) and a 5- to 10-fold increase of interleukin 2 (IL-2). Such a Thl response is believed to be important for intracellular pathogens such as viruses, mycobacteria, protozoa and tumors. Studies in vivo show that low concentrations of tucaresol enhance not only CD4+ Th cells in response to antigens but also CD 8+ CTL and that this response has a beneficial effect in antiviral and antitumor therapy in animal models. Mechanistically, formation of Schiff bases with tucaresol has been shown to greatly affect intracellular potassium and sodium ion concentrations by the co-stimulation of mitogen-activated protein kinase (MAP kinase) and thus activation of ion channels in T cells [62,102]. Some of these mechanistic features are depicted in Fig. 19. [Pg.165]


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