Specificity artificial substrates

Acetate is known to be a good carbon source for fungi and would be expected to be the ultimate degradation product of cutin (14). The effect of acetate on the production of cutinase by the T-8 strain of F. solani was examined and compared with that of glucose. Since previous studies showed that hydrolysis of the artificial substrate p-nitrophenylbutyrate, PNB, was specifically hydrolyzed by cutinase in the T-8 strain, this activity was used to measure cutinase levels (8). Figure 1 illustrates that basal levels of cutinase activity were detected in the growth medium when T-8 was grown on... 

Figure 4. Specific activity of cutinase for the T-8 parental strain and PNB-1 mutant strain after growth on medium containing 200 mg cutin. Enzyme activity was assayed with the artificial substrate PNB (Panel A) and with the natural substrate, [14C]-labelled cutin (Panel B). (Reproduced with permission from Ref. 13. 1986, American Society for Microbiology.)...

A distinct group of synthetic depsipeptides comprises of compounds that do not originate from natural product biodiversity several artificial substrates of peptidases and esterases belong to this group, as well as polydepsipeptides that are considered as potentially biodegradable polymeric materials. A specific feature of depsipeptide synthesis is the necessity to acylate a hydroxy acid component, which requires stronger activation of the amino acid component in comparison to normal peptide synthesis. Otherwise, the main principles of depsipeptide synthesis are similar to those of peptides. Frequently, formation of the ester... 

Mother nature has resolved the various limitations involved in multi-electron processes. Unique assemblies composed of cofactors and enzymes provide the microscopic catalytic environments capable of activating the substrates, acting as multi-electron relay systems and inducing selectivity and specificity. Artificially tailored heterogeneous and homogeneous catalysts as well as biocatalysts (enzymes and cofactors) are, thus, essential ingredients of artificial photosynthetic devices. 

The activities of intracellular enzymes give an indication of the activity of certain metabolic pathways. They are classically assayed by performing their specific reactions in vitro, using the conversion of natural or artificial substrates and often some additional detection reaction. The sample preparation procedure involves cell harvesting and preparation of cell extracts. A well-studied example is the metabolic shift in Clostridium acetobutylicum from acid to solvent production, the so-called solvent shift. Andersch et al. [48] studied the activities of 10 different enzymes involved in this shift, in batch cultivations where the shift is self-induced by the products formed, and under continuous culture conditions with an externally induced shift. 

Substrate specificity differences between boar acrosin and trypsin are not particularly manifest when using small substrates, but these enzymes show distinctly different kinetics of porcine ZP hydrolysis (34). The loss of 30% mass in the conversion from m - to m -acrosin has little effect on the kinetic analyses of inhibition and substrate preference with artificial substrates and small trypsin inhibitors, indicating that this excised portion of the enzyme contributes little to the topography of the active site (35). From Km analyses with amide and ester substrates of Arg and Lys, acrBSin prefers the Arg substrates over Lys, and Km differences between amide and ester substrates indicates that ac Ssin proceeds kinetically through a classical double displacement mechanism as does trypsin (36). 

Phage libraries have also been used to study the substrate specificity of enzymes by finding an improved artificial substrate. Coombs et al. (69) reported the detailed assessment of specificity for a serine protease belonging to the a-chymotrypsin family, the prostate specific antigen (PSA). They used both substrate optimization by singlepoint mutations and phage display libraries. The sequence of the 14-member substrate 10.2 (70) was used to start the iterative optimization process (Fig. 10.11) in which substitution or exchange of the PI, P2, or P2 residues increased the substrate affinity... 

However, there are some problems that are inherent in using this approach to biotransformation. Firstly, a xenobiotic transformation often involves just one step, e.g. a hydroxylation, whilst a biosynthetically-directed transformation may use a sequence of enzymatic steps. The artificial substrate may be a poor fit for some of these specific enzymes. Consequently, the overall yields may be rather poor. Secondly, unless the fermentation is modified in some way, the artificial exogenous substrate may be in competition with the natural metabolites, diminishing the yield and posing separation problems. Nevertheless, in several cases biosynthetically-directed biotransformations have been exploited to yield novel biologically-active compounds and useful biosynthetic information. 

The characterization and nomenclature of lipolytic enzymes are areas of considerable confusion. The literature is rich in references to enzyme activities, based on studies with limited natural and artificial substrates, that become established as specific enzymes for given substrate groups. Frequently, different workers have unwittingly studied the same enzyme under different names. In addition to presenting an up-to-date review of lipolytic enzymes in plants, the following discussion will attempt to remove some of the confusion that exists in this area. 

The modular and elegant programming characteristic of antibiotics synthetic process has provided us varieties of functional elements gathered from natural product biosynthetic pathways. Based on type of catalyzed reaction or specificity of substrate and product, all natural and artificial modified elanents can be categorized in synthetic... 

Studies with inhibitors of specific electron carriers, and with artificial substrates that oxidize or reduce one specific carrier, permit dissection of the electron transport chain into four complexes of electron carriers ... 

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