Hydrolysis inhibition

Synergism between the enzymes was shown to decrease with time during zymolysis. This may occur because the substrate for a particular glu-canase disappeared (but as the substrates were in excess in this case it is unlikely), or the products released during hydrolysis inhibited one or a number of the glucanases. 

Substrate or inducer Induction ratio Relative rate of hydrolysis" Inhibition constant K, (mM) Michaelis constant, K (mM) ... 

An enzyme (cathepsin) hydrolyzes L-glutamyl-L-tyrosine to carbobenzoxy-L-glutamic acid and L-tyrosine. It has been found (Frantz and Stephenson,/. Biol. Chem., 169,359,1947) that the glutamic acid formed in the hydrolysis, inhibits (competitively) the progress of the reaction by forming a complex with cathepsin. The course of the reaction is followed by adding tyrosme decarboxylase which evolves C02. 

Changing the solvent to ether prior to the base extraction step (to remove carboxylic acid formed by hydrolysis) inhibits emulsion formation, particularly with the higher aliphatic-substituted products. 

Figure 12 WLF plot for the hydrolysis kinetics of 2-(4-nitrophenoxy)tetrahydropyran, embedded in matrices of PHC glass formers in the neighbourhood of Tg. Note that the degrees of stabilisation provided by the glasses are in the reverse order as the glass transitions of the PHC i.e., dextran provides the largest (In k) decrease, but sucrose provides the most pronounced hydrolysis inhibition...

Figure 2.7 Hydrolysis inhibition by a-snbstitnted amino acid esters. The snbstituents at the a-carbon have a decisive effect on the hydrolytic stability of poly(organo)phosphazenes, shown here for valine...

Somatostatin is a tetradecapeptide of the hypothalamus that inhibits the release of pituitary growth hormone Its ammo acid sequence has been determined by a combination of Edman degradations and enzymic hydrolysis expenments On the basis of the following data deduce the pnmary structure of somatostatin... 

High purity acetaldehyde is desirable for oxidation. The aldehyde is diluted with solvent to moderate oxidation and to permit safer operation. In the hquid take-off process, acetaldehyde is maintained at 30—40 wt % and when a vapor product is taken, no more than 6 wt % aldehyde is in the reactor solvent. A considerable recycle stream is returned to the oxidation reactor to increase selectivity. Recycle air, chiefly nitrogen, is added to the air introducted to the reactor at 4000—4500 times the reactor volume per hour. The customary catalyst is a mixture of three parts copper acetate to one part cobalt acetate by weight. Either salt alone is less effective than the mixture. Copper acetate may be as high as 2 wt % in the reaction solvent, but cobalt acetate ought not rise above 0.5 wt %. The reaction is carried out at 45—60°C under 100—300 kPa (15—44 psi). The reaction solvent is far above the boiling point of acetaldehyde, but the reaction is so fast that Httle escapes unoxidized. This temperature helps oxygen absorption, reduces acetaldehyde losses, and inhibits anhydride hydrolysis. 

A critical component of the G-protein effector cascade is the hydrolysis of GTP by the activated a-subunit (GTPase). This provides not only a component of the amplification process of the G-protein cascade (63) but also serves to provide further measures of dmg efficacy. Additionally, the scheme of Figure 10 indicates that the coupling process also depends on the stoichiometry of receptors and G-proteins. A reduction in receptor number should diminish the efficacy of coupling and thus reduce dmg efficacy. This is seen in Figure 11, which indicates that the abiUty of the muscarinic dmg carbachol [51 -83-2] to inhibit cAMP formation and to stimulate inositol triphosphate, IP, formation yields different dose—response curves, and that after receptor removal by irreversible alkylation, carbachol becomes a partial agonist (68). 

Thiocyanate ion, SCN , inhibits formation of thyroid hormones by inhibiting the iodination of tyrosine residues in thyroglobufin by thyroid peroxidase. This ion is also responsible for the goitrogenic effect of cassava (manioc, tapioca). Cyanide, CN , is liberated by hydrolysis from the cyanogenic glucoside finamarin it contains, which in turn is biodetoxified to SCN. 

Thraustomycin. Thraustomycin and P-thraustomycin are isolated from S. exfoliatus (4). Although their stmctures have not been totally elucidated, hydrolysis of thraustomycin shows that it contains equimolar quantities of adenine, L-leucine, and a tetrahydroxymonocarboxyhc acid. Thraustomycin is a potent inhibitor of the fungus, Af. hiemallis (+), but does not inhibit bacteria. 

Fosfadecin (186) and fosfocytocin (187) are adenine and cytosine nucleotide antibiotics isolated from the culture filtrates of Pseudomonas viridiflava PK-5 and P. fluorescens PK-52, respectively (283). Hydrolysis produces fosfoxacin which is also isolated from the culture filtrates. Compounds (186) and (187) inhibit gram-positive and gram-negative bacteria. 

Phosphodiesterase Inhibitors. Because of the complexity of the biochemical processes involved in cardiac muscle contraction, investigators have looked at these pathways for other means of dmg intervention for CHF. One of the areas of investigation involves increased cycHc adenosine monophosphate [60-92-4] (cAMP) through inhibition of phosphodiesterase [9025-82-5] (PDE). This class of compounds includes amrinone, considered beneficial for CHF because of positive inotropic and vasodilator activity. The mechanism of inotropic action involves the inhibition of PDE, which in turn inhibits the intracellular hydrolysis of cAMP (130). In cascade fashion, cAMP-catalyzed phosphorylation of sarcolemmal calcium-channels follows, activating the calcium pump (131). A series of synthetic moieties including the bipyridines, amrinone and milrinone, piroximone and enoximone, [77671-31-9], C22H22N2O2S, all of which have been shown to improve cardiac contractiUty in short-term studies, were developed (132,133). These dmgs... 

Organophosphonates are similar to polyphosphates in chelation properties, but they are stable to hydrolysis and replace the phosphates where persistence in aqueous solution is necessary. They are used as scale and corrosion inhibitors (52) where they function via the threshold effect, a mechanism requiring far less than the stoichiometric amounts for chelation of the detrimental ions present. Threshold inhibition in cooling water treatment is the largest market for organophosphonates, but there is a wide variety of other uses (50). 

The addition of stabilizers to tetrachloroethylene inhibits corrosion of aluminum, iron, and zinc which otherwise occurs in the presence of water (12). Where water in excess of the solubiUty limit is present, forming separate layers, hydrolysis and corrosion rates increase. System design and constmction materials should consider these effects. 

The hydrolysis of nitriles can be carried out with either isolated enzymes or immobilized cells. Eor example, resting cells of P. chlororaphis can accumulate up to 400 g/L of acrylamide in 8 h, provided acrylonitrile is added gradually to avoid nitrile hydratase inhibition (116). The degree of acrylonitrile conversion to acrylamide is 99% without any formation of acryUc acid. Because of its high efficiency the process has been commercialized and currentiy is used by Nitto Chemical Industry Co. on a multithousand ton scale. 

Fermentation can be combined with other operations. For example, feedback inhibition of enzymatic hydrolysis of cellulose can be relieved by removal of the product glucose by fermentation as it forms. This is teni ed. simultaneou.s-saccharification-fermentation (SSF). 

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