Cooperation of enzymes

Kauss, H. and Swanson, A.L. (1969) Cooperation of enzymes responsible for polymerization and methylation in pectin biosynthesis. ZJ aturforsch. 24 28-33. 

Neet, K. E. (1995) Cooperativity of enzyme function equilibrium and kinetic aspects, in Purich, D. L. (eds.), Methods in Enzymology, 249, Enzyme Kinetics and Mechanisms, Part D, Acad. Press, San-Diego, 519-567. 

The cooperation of enzymes at membranes was found to vary between two extremes a tight complex which does not even accept the intermediate if it is added externally and, on the other hand, loose associations V hich are gradually lost upon cell disintegration and therefore are difficult to define. 

Chapter 5 also demonstrates that a combination of Lewis-acid catalysis and micellar catalysis can lead to accelerations of enzyme-like magnitudes. Most likely, these accelerations are a consequence of an efficient interaction between the Lewis-acid catalyst and the dienophile, both of which have a high affinity for the Stem region of the micelle. Hence, hydrophobic interactions and Lewis-acid catalysis act cooperatively. Unfortunately, the strength of the hydrophobic interaction, as offered by the Cu(DS)2 micellar system, was not sufficient for extension of Lewis-acid catalysis to monodentate dienophiles. 

The I I cleaning procedures as a whole, compared with household laundering, are characterized by huge variations in the composition of the soils, types of surface to which they adhere, cleaning time available, etc. The optimum choice of enzyme type and dosage level normally has to be established through a cooperation between the customer (end user), manufacturer of the detergent, and enzyme producer. 

The basic kinetic properties of this allosteric enzyme are clearly explained by combining Monod s theory and these structural results. The tetrameric enzyme exists in equilibrium between a catalytically active R state and an inactive T state. There is a difference in the tertiary structure of the subunits in these two states, which is closely linked to a difference in the quaternary structure of the molecule. The substrate F6P binds preferentially to the R state, thereby shifting the equilibrium to that state. Since the mechanism is concerted, binding of one F6P to the first subunit provides an additional three subunits in the R state, hence the cooperativity of F6P binding and catalysis. ATP binds to both states, so there is no shift in the equilibrium and hence there is no cooperativity of ATP binding. The inhibitor PEP preferentially binds to the effector binding site of molecules in the T state and as a result the equilibrium is shifted to the inactive state. By contrast the activator ADP preferentially binds to the effector site of molecules in the R state and as a result shifts the equilibrium to the R state with its four available, catalytically competent, active sites per molecule. 

FIGURE 19.8 At high [ATP], phosphofruc-tokinase (PFK) behaves cooperatively, and the plot of enzyme activity versus [frnctose-6-phos-phate] is sigmoid. High [ATP] thus inhibits PFK, decreasing the enzyme s affinity for frnc-tose-6-phosphate. 

The Hill Equation Describes the Behavior of Enzymes That Exhibit Cooperative Binding of Substrate... 

The Ca binding sites of the enzyme remained functional after DEPC treatment [368], but the cooperativity of Ca binding seen in native Ca -ATPase was abolished. The Ca " binding to the DEPC-modified Ca " -ATPase could be described in terms of two independent Ca binding sites with Xca of 14 uM and 0.5 (iM, respectively. The phosphorylation of DEPC-modified Ca -ATPase followed closely the saturation of the site with the higher Ca affinity [368]. 

Lack of perfect specificity in carrier-solute recognition provides for the possibility that structurally similar solutes may compete for carrier availability. Analysis of competitive [Eq. (18)] and noncompetitive [Eq. (19)] inhibition as well as cooperativity effects (allosteric modulation by structurally dissimilar solutes) on carrier-mediated solute flux is equivalent to assessment of the velocity of enzyme reactions. 

K. H. Meyer s scientific life took a new direction when a large segment of his laboratory was devoted to the study of the degradative enzymes of starch, the amylases. With the cooperation of Bernfeld first, then of E. H. 

A growing number of protein crystal structures has provided solid evidence that in many phosphoesterase enzymes, two and sometimes even three, di- or trivalent metal ions are involved in substrate transformation. Consequently, the high catalytic efficiency is, in part, the result of a perfectly coordinated catalytic cooperation of the metal ions. Dinu-clear phosphoiyl transfer enzymes have been discussed thoroughly in recent reviews [1-3]. Therefore, this chapter (Section 2) only gives a brief description of enzymes for which two-metal promotion of phos-phoester hydrolysis was proposed on the basis of detailed mechanistic or crystallographic studies (Table 1). 

Flodstrom, S., L. Wamgard, S. Ljungquist, and U.G. Ahlborg. 1988. Inhibition of metabolic cooperation in vitro and enhancement of enzyme altered foci incidence in rat liver by the pyrethroid insecticide fenvalerate. Arch. Toxicol. 61 218-223. 

Two other general ways of treating micellar kinetic data should be noted. Piszkiewicz (1977) used equations similar to the Hill equation of enzyme kinetics to fit variations of rate constants and surfactant concentration. This treatment differs from that of Menger and Portnoy (1967) in that it emphasizes cooperative effects due to substrate-micelle interactions. These interactions are probably very important at surfactant concentrations close to the cmc because solutes may promote micellization or bind to submicellar aggregates. Thus, eqn (1) and others like it do not fit the data for dilute surfactant, especially when reactants are hydrophobic and can promote micellization. 

Excision Repair. Some groups of enzymes (light-independent) are apparently organized to act cooperatively to recognize DNA lesions, remove them, and correctly replace the damaged sections of DNA. The most comprehensively studied of these is the excision repair pathway. 

In order for an equilibrium to exist between E -E S and ES, the rate constant kp would have to be much smaller than k i However, for the majority of enzyme activities, this assumption is unlikely to hold true. Nevertheless, the rapid equilibrium approach remains a most useful tool since equations thereby derived often have the same form as those derived by more correct steady-state approaches (see later), and although steady-state analyses of very complex systems (such as those displaying cooperative behavior) are almost impossibly complicated, rapid equilibrium assumptions facilitate relatively straightforward derivations of equations in such cases. 

To understand the basic role served by vitamins in human health, we need to retreat to chapter 9 for a moment. We discussed there the nature of an amazing group of proteins, the catalysts of living systems, enzymes. Many enzymes are perfectly happy to work by themselves and they do work by themselves. Others, in contrast, require a partner for their catalytic functions. These partners are known by the generic name of coenzymes. Basically, they cooperate with enzymes in getting the catalytic job accomplished. Although his name implies that he worked... 

All these observations prompt the question as to what the redox potentials are for the c and di hemes under equilibrium conditions. This issue is currently under study, and all that can be said here is that the enzyme does not give a straightforward redox titration. In particular, and in contrast to the observations made under pulse radiolysis conditions, the c and di hemes titrate together, suggesting a cooperativity of behavior between them (see note added in proof). It remains to elucidate the molecular basis for this effect. 

Thiamine diphosphate (TPP, 3), in cooperation with enzymes, is able to activate aldehydes or ketones as hydroxyalkyl groups and then to pass them on to other molecules. This type of transfer is important in the transketo-lase reaction, for example (see p. 152). Hydroxyalkyl residues also arise in the decarboxylation of 0x0 acids. In this case, they are released as aldehydes or transferred to lipoamide residues of 2-oxoacid dehydrogenases (see p. 134). The functional component of TPP is the sulfur- and nitrogen-containing thiazole ring. 

The increase in energy content of an atom, ion, or molecular entity or the process that makes an atom, ion, or molecular entity more active or reactive. In enzymology, activation often refers to processes that result in increased enzyme activity. For example, increasing temperature often can have a positive effect on enzyme activity (See Arrhenius Equation). Other examples of enzyme activation include (1) proteolysis of zymogens (2) alterations in ionic strength (3) alterations due to pH changes (4) activation in cooperative systems (5) lipid or membrane interface activation (6) metal ion effects (7) autocatalysis and (8) covalent modification. 

Should one use Hill plots to examine the initial velocity behavior of enzymes Because infinite cooperativity is... 

Slow transitions produced by enzyme isomerizations. This behavior can lead to a type of cooperativity that is generally associated with ligand-induced conformational changes . A number of enzymes are also known to undergo slow oligomerization reactions, and these enzymes may display unusual kinetic properties. If this is observed, it is advisable to determine the time course of enzyme activation or inactivation following enzyme dilution. See Cooperativity Bifurcation Theory Lag Time... 

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