Transference, role

Heat pipes are used to perform several important heat-transfer roles ia the chemical and closely aUied iadustries. Examples iaclude heat recovery, the isothermaliziag of processes, and spot cooling ia the mol ding of plastics. In its simplest form the heat pipe possesses the property of extremely high thermal conductance, often several hundred times that of metals. As a result, the heat pipe can produce nearly isothermal conditions making an almost ideal heat-transfer element. In another form the heat pipe can provide positive, rapid, and precise control of temperature under conditions that vary with respect to time. 

His35 to ligated His46 may be important in an electron transfer role or in His35 exercising some conformational control of the active site. The reduction potential of P. aeruginosa azurin increases from 300 mV (pH 8) to 360 mV (pH 5), which is believed to be related to His35 protonation. A pK of 6.6 is observed for this process, or alternatively pK s for azurin in the oxidized (6.1) and reduced (7.2) forms can be obtained [56]. 

Slikker W Jr Miller RK (1994) Placental metabolism and transfer Role in developmental toxicology. In Kimmel CA Buelke-Sam J ed. Developmental toxicology, 2nd ed. New York. Raven Press, pp 245-283. 

The electron transfer role of vanadium has possible relevance to vanadium bro-moperoxidase, although this system and V-BrPO differ in that V-BrPO requires dihydrogen peroxide for catalytic activity. A speculative catalytic cycle has been proposed to be... 

Mah, C. et al. (1998). Adeno-associated virus type 2-mediated gene transfer Role of epidermal growth factor receptor protein tyrosine kinase in transgene expression. J. Virol. 72, 9835-9843. 

How does an ionophore transfer an ion across a membrane The ionophore binds the ion on one side of the membrane in its polar interior. It can then move across the membrane because its hydrophobic exterior interacts with the hydrophobic tails of the phospholipid. The ionophore then releases the ion on the other side of the membrane. This ion-transfer role is essential for normal cell function. This process is illustrated in Figure 3.8. 

Graphite or carbon, as a support, can induce different properties in a catalyst by, for example, promoting spill-over or affecting catalyst geometry. At the same time, however, graphite (in particular) can act as an electron transfer agent and, as a result, become involved in reaction as a co-catalyst. This electron transfer role has been noted previously in connection with cases where carbon itself is the main catalyst. As a co-catalyst with another material, the electron transfer properties of carbons have been suggested to be important in a variety of reactions. 

The 1-Fe rubredoxins are single polypeptide chain proteins of about 55 amino acid residues and 6,000 dalton molecular weight. The primary structure of the Microccus aerogenes (220, 221) and Peptostreptoccus elsdenii (210) proteins have been determined. The two amino acid sequences (Fig. 11) reveal a relatively high mutation frequency, with a noticeable conservancy around the four cysteinyl residues which are critically involved in binding the iron and hence in the proposed electron transfer role of the protein (210). Another curious feature of the anaerobic rubredoxins is the presence of N-formyl methionine as N-terminus amino acid (222). Synthesis of the polypeptide is in progress (223). 

The structures shown in Figures 1 and 2 illustrate several general structural themes that facilitate rationalization of functional diversity. Exclusive cysteinyl ligation is generally observed in centers that function purely in electron transfer roles. Histidine, aspartate, serine, or backbone amide N ligation at a unique Fe site are occasionally encountered in clusters that function in electron transport and serve to modify redox potentiaH and gate electron transport,or facilitate coupling of proton and electron transport. 

Treatment of the enzyme with acyl phosphate in the complete absence of reduced cofactor has allowed the thiol enzyme derivative to be prepared and separated from its reaction mixture. This in turn has permitted considerable characterization of the enzyme thiol. No special cofactor is involved. The thiol of a cysteine residue from the main peptide chain of the enzyme provides the reactive centre. This enzyme demonstrates that the acyl transfer role of thioesters in biological systems is not restricted to phosphopantetheine and dihydrolipoate derivatives. The reactions of the... 

Mutational studies implicated aspartate (Asp98) and histidine (His255) amino acid residues to be directly involved in the catalytic activity (187,188). An X-ray structure reveals that Asp98 forms a hydrogen bond to both a bound nitrite and NO (188). Also, His255 is proposed to have a proton transfer role in the... 

Reactions of nitric and nitrous acid with hydroxylamine will be discussed in a later section. The bulk of published work has been concerned with nitration of organic substrates, such as cinnamic acids and 2-iodo-1,3,5-trialkylbenzenes. Evidence has been produced to show the wider generality of the electron transfer role for nitrous acid in the catalysis... 

Zhang, J. Klinman, J.P. Enzymatic Methyl Transfer Role of an Active Site Residue in Generating Active Site Compactio that Correlates with Catalytic Efficiency. J. Am. Chem. Soc. 2011,133, 17134-17137. 

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