Glycerol enzyme-catalyzed reactions

Metabolism of Glycerol Glycerol obtained from the breakdown of fat is metabolized by conversion to dihydroxy-acetone phosphate, a glycolytic intermediate, in two enzyme-catalyzed reactions. Propose a reaction sequence for glycerol metabolism. On which known enzyme-catalyzed reactions is your proposal based Write the net equation for the conversion of glycerol to pyruvate according to your scheme. 

An iniponani propeny of enzymes is that they are specific that is. one enzyme can usually catalyze only one type of reaction. For example, a protease hydrolyzes only bonds between specific amino acids in proteins, an amylase works on bonds between glucose molecules in starch, and lipa.se attacks fats, degrading them to fatty acids and glycerol, Con.sequently, unwanted products are easily controlled in enzyme-catalyzed reactions. Enzymes are produced only by living organisms, and commercial enzymes are generally produced by bacteria. Enzymes usually work (i.e., catalyze reactions) under... 

Fig. 4.1 Simplified representation of the main metabolic activity of the form of the parasite Trypanosoma brucei found in the bloodstream. The different degrees of shading distinguish the four different compartments in the system, including the blood of the host, which supplies the glucose and inorganic phosphate needed by the parasite for its metabohsm, and receives the pyruvate and glycerol that it excretes. The shaded circles represent the different metabolites, connected by hues to indicate enzyme-catalyzed reactions...

Each of the two triose phosphates participates in a different enzymatic oxidation-reduction system. Dihydroxyacetone phosphate may be reduced to glycerol phosphate and phosphoglyceraldehyde may be oxidized to phosphoglyceric acid. Both of these are enzyme-catalyzed reactions in which the pyridine nucleotide, DPN, participates. The two reactions may thus be linked by the coenzyme, and in some crude extracts glycerol phosphate and phosphoglyceric acid may accumulate as end-products of fermentation. 

You might note that C2 of glycerol is a prochiral center with two identical arms, a situation similar to that of citrate in the citric acid cycle (Section 22.4). As is typical for enzyme-catalyzed reactions, the phosphorylation of glycerol is selective. Only the pro-R arm undergoes reaction, although this can t be predicted in advance. 

In the first stage of fat catabolism, the fat s three ester groups are hydrolyzed by an enzyme-catalyzed reaction to glycerol and three fatty acid molecules (Section 16.9). 

A Streptomyces enzyme that catalyzes hydrolysis of capsaicin is described by Koreishi et The substrate is an A -vanillyl aliphatic amide, and the authors found that their enzyme also accepted A lauroyl amino acids as substrates. The enzyme was used successfully to catalyze the reaction in the opposite direction, driving the equilibrium toward synthesis by running it in buffer containing 78% glycerol. Yields of 5-40% were obtained for a wide range of natural L-amino acids. In the case of L-lysine the enzyme catalyzed acylation at both amino groups, with a clear preference for the e-NH2. 

The problem with enzyme catalyzed reversible transesterifications as an approach to biochemical resolution is that due to the reversible nature of the reaction, the enantiomeric excess of the desired product in the forward reaction decreases as the reverse reaction proceeds. As in hydrolytic reactions, the irreversible transesterification offers a better process for optimization of the transformation and for recovery of the product. Furthermore, there is no product inhibition observed in the irreversible process. Both enantiomers can be converted to glycerol acetonide with known procedures. 

This enzyme catalyzes the reaction of an acyl-CoA derivative with l-acyl-vn-glycerol 3-phosphate to generate coenzyme A and l,2-diacyl-5 n-glycerol 3-phosphate. The animal enzyme is reported to be specific for the transfer of unsaturated fatty acyl groups. Interestingly, the acyl-[acyl-carrier-protein] can also act as an acyl donor. 

Energy production from triacylglycerols starts with their hydrolysis into free fatty acids and glycerol. Enzymes called lipases, which catalyze the reaction, carry out this hydrolysis. 

Two different types of enzymatic time-temperature integrators are described. The first, under the tradename of I-point, is based on a lipase-catalyzed hydrolysis reaction (125). The lipase is stored in a nonaqueous environment containing glycerol. The indicator contains two components that are mixed when the indicator is activated. The operating principle is as follows Upon activation, two volumes of reagents are mixed with each other. Lipase is thereby exposed to its substrate, here a triglyceride. At low temperatures there will be almost no hydrolytic reaction. As the temperature increases, hydrolysis accelerates and protons are liberated. A pH indicator is dissolved in the system. The indicator is selected to shift color after a certain amount of acid has been liberated by the enzyme-catalyzed process. Since the catalytic activity is influenced both by temperature and time, this indicator strip is said to be a time-temperature integrator. 

All assay methods are based on the forward ALD-catalyzed reaction. Both photometric fixed-time and continuous-monitoring procedures have been developed. In the analytical approach on which all the commonly used procedures and kits are based, the ALD reaction is coupled with two other enzyme reactions. Triosephosphate isomerase (EC 5.3.1.1) is added to ensure rapid conversion of all GLAP to DAP. Glycerol-3-phosphate dehydrogenase (EC 1.1.1.8) is added to reduce the DAP to glycerol-3-phosphate, with NADH acting as hydrogen donor. The decrease in NADH concentration is then measured. 

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