Reaction control proteins

Molecular imprinting is not limited to organic polymer matrices, but can also be applied to silica-based materials and even proteins. Proteins freeze-dried in the presence of a transition state analogue as template have been used successfully as catalysts, e.g., for the dehydrofluorination of a fluorobutanone. For instance, lyophilized 3-lactoglobulin imprinted in this manner with N-isopropyl-N-ni-trobenzyl-amine could accelerate the dehydrofluorination by a factor of 3.27 compared to the non-imprinted protein see Table 5 [62]. In a similar procedure, BSA was imprinted with N-methyl-N-(4-nitrobenzyl)-S-aminovaleric acid and showed an enhancement of the catalytic effect by a factor of 3.3 compared to the control protein for the same reaction see Table 5 [113]. 

Chapter 4 describes the in vitro reaction of glucose wifh demineralized dentin. Preliminary tests revealed that use of disfilled insfead of deionized water accelerated browning, consistent with the effect of frace metals on the Maillard reaction. The yellow discolored slices were more resistant than controls to pepsin-mediated breakdown, but not to trypsin-mediated breakdown. It would be worthwhile to investigate proteolysis of denfin collagen covalently bound by the Maillard reaction to proteins, which penetrate into a caries lesion. 

The disk electrode potential is controlled to bring about the reaction indicated for A. The ring is held at a potential to cause B to react to C. Then the fraction of B obtained on the ring is N. Knowledge of this helps in understanding the formation of C, hence the mechanism of the overall reaction. There are many reactions of this type (called E. C.E. reactions). Some proteins undergo bromination in this sequence, the bromina-tion step reaction being at B. 

Antioxidant Control protein oxidation Usually not employed, molecular reactions in the lyo cake are greatly retarded... 

The control of glycogen phosphorylase by the phosphorylation-dephosphorylation cycle was discovered in 1955 by Edmond Fischer and Edwin Krebs50 and was at first regarded as peculiar to glycogen breakdown. However, it is now abundantly clear that similar reactions control most aspects of metabolism.51 Phosphorylation of proteins is involved in control of carbohydrate, lipid, and amino acid metabolism in control of muscular contraction, regulation of photosynthesis in plants,52 transcription of genes,51 protein syntheses,53 and cell division and in mediating most effects of hormones. 

Among the more important factors affecting reactions with proteins, pH is the most important since it controls the distribution of potentially reactive side chains between reactive and unreactive ionization states (see Table II). Iodoacetic acid is a commonly used reagent in protein modifications and serves as an example. At low pH values (such as 2-5)... 

Balabin, I.A. and Onuchic, J.N. (2000) Dynamically controlled protein tunneling pathes in photosynthetic reaction centers, Science 290, 114- 117. 

The reactions of proteins in alkaline solution are very important from a number of standpoints. We have already discussed several uses of alkali treatment in food processing in the introduction. When contact between the food and alkali is kept to a minimum at the lowest temperature possible with adequate control of mixing, etc. there is presently no apparent reason to discontinue its use. Low levels of lysinoalanine occur in food which has been processed in the absence of added alkali, even at pH 6 and in the dry state (20). For example, the egg white of an egg boiled three minutes contained 140 ppm of lysinoalanine while dried egg white powder contained from 160 to 1820 ppm of lysinoalanine depending on the manufacturer (20). No lysinoalanine was found in fresh egg white, 3 Elimination and addition of lysine to the double bond of dehydroalanine reduce the level of the essential amino acid lysine. This can be prevented by adding other nucleophiles such as cysteine to the reaction. Whether lysinoalanine (and other compounds formed by addition reactions) is toxic at low levels in humans is not known. 

The metabolically important functions of the Bn-derivatives are directly concerned either with enzymatically controlled organometalhc reactions involving protein-bound adenosylcobamides (such as coenzyme B12, (3)), or methyl-Co -corrinoids (such as methylcobalamin, (4)), or with enzyme-controlled redox reactions. Studies on the underlying biologically relevant organometalhc chemistry of the Bi2-coenzymes in homogeneous (protic) solution, as well as the characterization of the enzymatic processes themselves have attracted considerable interest. ... 

Investigations of protein-protein ET reactions have provided important insights into biological electron flow [10-14]. Natural systems, however, often are not amenable to the systematic studies that are required for evaluation of the key ET parameters 2 and Nab- A successful alternative approach involves measurements of ET in metalloproteins that have been labeled with redox-active molecules [15-19]. By varying the binding site and chemical composition of the probe molecule, it has been possible to elucidate the factors that control the rates of long-range ET reactions in proteins. 

Conformational changes could control ET reactions in proteins. The rates of such changes often are in the same range as ET rates for example, the T-R transition in hemoglobin occurs at a rate of approximately 2 X 10 s (112). Hoffman and Ratner (66,67) have pointed out that a way to test for conformational control of an ET reaction is to measure the reaction rate at different driving forces. If the rate stays the same, the ET reaction is conformationally controlled. If it does not, it is not confor-mationally controlled. No evidence for conformation control exists for ET in ruthenium-modified proteins on this basis. Data from both ruthenated His-33 in horse heart cytochrome c (126) and ruthenated His-48 in myoglobin (103) show that the rate changes with AG° in a manner consistent with Marcus theory. 

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