In vitro enzyme catalyzed

Pseudomonine (Fig. 27, 76) is produced by Pseudomonas fluorescens strains (7, 228) and by P. entomophila, where it can act as a secondary siderophore (209). The substituents on C-4 and C-5 of the isoxazolinone ring are in trans positions (333). The complex formation has not been studied. In vitro enzyme-catalyzed synthesis studies (333,388) showed that initially the intermediate pre-pseudomonine (Fig. 24, 79) is formed, which non-enzymatically rearranges to pseudomonine. 

Table IV. In Vitro Enzyme-Catalyzed Hydrolytic Modifications of Food Proteins...

Relatively very few reports exist on use of biocatalytic methodologies for carrying our surface modification of SAMs. Use of enzymes in organic synthesis (77) and polymer science (78) is well established and has been discussed elsewhere in comprehensive reviews. The rapidly increasing interest in in vitro enzyme-catalyzed organic and polymeric reactions has been due to the fact that several families of enzyme utilize and transform not only their natural substrates but also a wide range of unnatural compounds to yield a variety of useful... 

In vitro enzyme-catalyzed ROP in a nonaqueous medium has been extensively investigated during the past 15 years (see also Chapter 15). The benefits of using enzymes as catalysts instead of nonenzymatic methods include ... 

Hubl, U. and Stevenson, D.E. (2001) In vitro enzymic synthesis of mammalian liver xenobiotic metabolites catalyzed by ovine liver microsomal cytochrome P450. Enzyme and Microbial Technology, 29, 306-311. 

To understand why it is often difficult to interpret in vitro enzymes assays, it is useful to consider the principles of metabohc control theory, derived from engineering control theory (Raven, 1981). Consider a series of enzyme catalyzed reactions, where a, b, c, and d represent substrates and or products of reactions catalyzed by enzymes represented by A, B, and C ... 

The metabolisms of yeasts and microorganisms ensure a sufficient supply of the NAD(P)H coenzyme during fermentative reductions. Since the NAD(P)H needed for in vitro reductions catalyzed by isolated enzymes is expensive, it is used in catalytic amounts only, and continuously regenerated from the inactive pyridinium form of NAD or NADP by an economical recycling system. ... 

An early indication that a widely used agricultural chemical might be metabolized to a nonpolar conjugate in plants came from an in vitro enzyme study with C-labeled surfactants of the Triton family. A crude particulate enzyme preparation from com shoots catalyzed the formation of fatty acid ester conjugates from the two 1"c-labeled polyethoxylated surfactants indicated below (Equation 32). The ester conjugates were formed primarily from palmitic and linoleic acids 0851). They were identified by mass spectrometry and by GLC analysis of hydrolysis products (J48). In vljro, rice and... 

Though the symptoms of the biological action of coprine and disulhram are similar, it was demonstrated that the mechanisms of action are different. Contrary to cyclopropanone hydrate, coprine inhibits mouse liver aldehyde dehydrogenase only in vivo but not in vitro. Based on this observation Wiseman and Abeles (429) assumed that coprine itself is inactive in vivo but is activated by hydrolysis to give initially cyclopropanone hemia-minal and ultimately cyclopropanone hydrate. After enzymatic dehydration to cyclopropanone, this compound forms a kinetically stable thiohe-miketal with the enzyme active-site thiols, leading to inactivation of aldehyde dehydrogenase in the enzyme-catalyzed oxidation of acetaldehyde to acetic acid (Scheme 97). 

This special volume on the enzyme-catalyzed synthesis of polymers focuses on various methods of polymer synthesis using enzymes as catalysts. There are three cases for such synthetic processes (1) In hving cells (in vivo) enzymes catalyze the synthesis of all biopolymers besides other biological substances via biosynthetic (metabolic) pathways, hi test tubes (in vitro) enzymatic catalysis is achieved for the synthesis of polymers via (2) biosynthetic pathways or (3) non-biosynthetic pathways. The present volume is concerned with case (3). Therefore, studies such as the synthesis of polyesters via fermentation using micro-organisms and synthesis of proteins using E. coli are not included. 

We 11 see numerous examples of both reaction types m the following sections Keep m mind that m vivo reactions (reactions m living systems) are enzyme catalyzed and occur at far greater rates than those for the same transformations carried out m vitro ( m glass ) m the absence of enzymes In spite of the rapidity with which enzyme catalyzed reactions take place the nature of these transformations is essentially the same as the fundamental processes of organic chemistry described throughout this text... 

---