Enzymes hydrolase

Hydrolases. Enzymes catalysing the hydrolytic cleavage ofC —O, C —N and C —C bonds. The systematic name always includes hydrolase but the recommended name is often formed by the addition of ase to the substrate. Examples are esterases, glucosidases, peptidases, proteinases, phospholipases. Other bonds may be cleaved besides those cited, e.g. during the action of sulphatases and phosphatases. 

The specificity of enzyme reactions can be altered by varying the solvent system. For example, the addition of water-miscible organic co-solvents may improve the selectivity of hydrolase enzymes. Medium engineering is also important for synthetic reactions performed in pure organic solvents. In such cases, the selectivity of the reaction may depend on the organic solvent used. In non-aqueous solvents, hydrolytic enzymes catalyse the reverse reaction, ie the synthesis of esters and amides. The problem here is the low activity (catalytic power) of many hydrolases in organic solvents, and the unpredictable effects of the amount of water and type of solvent on the rate and selectivity. 

Hydrolase enzymes catalyze the hydrolysis of a substrate and are most commonly coupled with potentiometericela trodes The pioneering work in this field focussed on de loping an enzyme electrode for the determination of urea. Urease catalyzes the hydrolysis of urea to ammonium and bicarbonate ions according to the reaction detailed below. 

The power of the pooled GST fusion protein approach will increase as new biochemical reagents and assays become available. The development of chemical probes for biological processes, termed chemical biology, is a rapidly advancing field. For example, the chemical synthesis of an active site directed probe for identification of members of the serine hydrolase enzyme family has recently been described (Liu et al., 1999). The activity of the probe is based on the potent and irreversible inhibition of serine hydrolases by fluorophosphate (FP) derivatives such as diisopropyl fluorophosphate. The probe consists of a biotinylated long-chain fluorophosphonate, called FP-biotin (Liu et al., 1999). The FP-biotin was tested on crude tissue extracts from various organs of the rat. These experiments showed that the reagent can react with numerous serine hydrolases in crude extracts and can detect enzymes at subnanomolar... 

It is possible to increase colour yields on wool by the use of protease or hydrolase enzymes (section 10.4.2). Although some improvement in yield was observed at temperatures as low as 50 °C, the increase was insufficient to be of commercial interest, but yields with enzyme at 85 °C were close to those obtained without enzyme at 100 °C [25]. 

However, the exquisite selectivity of hydrolase enzymes is, perhaps, best illustrated by their ability to produce optically active compounds from prochiral and mew-substrates. In both these cases a theoretical yield of 100% for optically pure material is possible (Scheme 4)[12, 13]. 

Hydrolases. Enzymes that catalyse hydrolytic reactions. 

As explained in the Introduction, alkene oxides (10.3) are generally chemically quite stable, indicating reduced reactivity compared to arene oxides. Under physiologically relevant conditions, they have little capacity to undergo rearrangement reactions, one exception being the acid-catalyzed 1,2-shift of a proton observed in some olefin epoxides (see Sect. 10.2.1 and Fig. 10.3). Alkene oxides are also resistant to uncatalyzed hydration, thus, in the absence of hydrolases enzymes, many alkene oxides that are formed as metabolites are stable enough to be isolated. 

L. W. Wormhoudt, J. N. Commandeur, N. P. Vermeulen, Genetic Polymorphisms of Human V-Acetyltransferase, Cytochrome P450, Glutathione 5-Transferase, and Epoxide Hydrolase Enzymes Relevance to Xenobiotic Metabolism and Toxicity , Crit. Rev. Toxicol. 1999, 29, 59 - 124. 

G. M. Lacourciere, R. N. Armstrong, Microsomal and Soluble Epoxide Hydrolases are Members of the Same Family of C-X Bond Hydrolase Enzymes , Chem. Res. Toxicol. 1994, 7, 121 - 124. 

Scheme 1.18 Hydrolysis of valaciclovir by a human hydrolase enzyme...

The cholinesterases, acetylcholinesterase and butyrylcholinesterase, are serine hydrolase enzymes. The biological role of acetylcholinesterase (AChE, EC 3.1.1.7) is to hydrolyze the neurotransmitter acetylcholine (ACh) to acetate and choline (Scheme 6.1). This plays a role in impulse termination of transmissions at cholinergic synapses within the nervous system (Fig. 6.7) [12,13]. Butyrylcholinesterase (BChE, EC 3.1.1.8), on the other hand, has yet not been ascribed a function. It tolerates a large variety of esters and is more active with butyryl and propio-nyl choline than with acetyl choline [14]. Structure-activity relationship studies have shown that different steric restrictions in the acyl pockets of AChE and BChE cause the difference in their specificity with respect to the acyl moiety of the substrate [15]. AChE hydrolyzes ACh at a very high rate. The maximal rate for hydrolysis of ACh and its thio analog acetyl-thiocholine are around 10 M s , approaching the diffusion-controlled limit [16]. 

Lipases belong to the subclass of serine hydrolases, and their structure and reaction mechanism are well understood. Their common a/p-hydrolase enzyme fold is characterized by an a-helix that is connected with a sharp turn, referred to as the nucleophilic elbow, to the middle of a P-sheet array. All lipases possess an identical catalytic triad consisting of an Asp or Gin residue, a His and a nucleophilic Ser [14]. The latter residue is located at the nucleophilic elbow and is found in the middle of the highly conserved Gly—AAl—Ser—AA2—Gly sequence in which amino acids AAl and AA2 can vary. The His residue is spatially located at one side of the Ser residue, whereas at the opposite side of the Ser a negative charge can be stabilized in the so-called oxyanion hole by a series of hydrogen bond interactions. The catalytic mechanism of the class of a/P-hydrolases is briefly discussed below using CALB as a typical example, since this is the most commonly applied lipase in polymerization reactions [15]. 

It acts by competitively inhibiting pancreatic alphaamylase and intestinal alpha glucosidase hydrolase enzymes. 

You are concerned about the longevity of the herbicide, linuron, leaching into a river from some neighboring farmland. Given the structure of this urea derivative, you expect it will be biodegraded via a hydrolysis mechanism. You recall a report of a hydrolase enzyme from a common bacterium that exhibits a half-saturation constant, KMM, for linuron of 2 /tM and a maximum degradation rate, Vmax, for linuron of 2500 /nmol kg-1 protein s l. 

Catabolism of some glycosphingolipids. The glycosyl hydrolase enzymes involved in these reactions are localized in the lysosomes. 

The four-step synthesis of a, -diaminocaprolactam shown in Figure 5.29 is part ofa chemoenzymatic route to (S)-lysine, an essential amino add in our diet [135], The racemic caprolactam (azepan-2-one) product is then hydrolyzed selectively to (S)-lysine, using an immobilized (S)-hydrolase enzyme. 

The types of enzymes that bring about hydrolysis are hydrolase enzymes. Like most enzymes involved in the metabolism of xenobiotic compounds, hydrolase enzymes occur prominently in the liver. They also occur in tissue lining the intestines, nervous tissue, blood plasma, the kidney, and muscle tissue. Enzymes that enable the hydrolysis of esters are called esterases, and those that hydrolyze amides are amidases. Aromatic esters are hydrolyzed by the action of aryl esterases and alkyl esters by aliphatic esterases. Hydrolysis products of xenobiotic compounds may be either more or less toxic than the parent compounds. 

Benzene oxide may be hydrated through the action of epoxide hydrolase enzyme,... 

Keywords L-asparaginase hydrolase enzyme engineering leukaemia thermal stability. 

Lysosomes in animal cells are bounded by a single membrane. They have an acidic internal pH (pH 4-5), maintained by proteins in the membrane that pump in H+ ions. Within the lysosomes are acid hydrolases enzymes involved in the degradation of macromolecules, including those internalized by endocytosis. 

FIGURE 19.1 General reactions of hydrolase enzymes. In the same group as nitrilase enzymes are the amidases. This includes amino acid amidase ... 

Until the last decade or so, the only synthetically useful catalytic asymmetric acyl transfer processes were biotransformations using hydrolase enzymes particularly lipases and esterases [24]. Various lipases and esterases provide high levels of stereoselectivity (s) for the acylative KR and ASD of a wide variety of sec-alcohols and some amines, although the latter transformations have been less thoroughly explored [25-28]. However, the preparative use of enzymes is associated with a number of well-documented limitations, including their generally... 

---