Other natural substrates

Specialized substrates include twigs for bioassays of sawflies (All Benjamin 1976 Ohigashi et al. 1981) and bark beetles (Ascher et al. 1975). Blocks of wood (Lenz Williams 1980), board, logs, and paper towel disks (Rust Reierson 1977) have been used for bioassays involving termites. The original references should be consulted for detailed descriptions of methods. 

Food deprivation prior to the bioassay may be desirable to increase overall activity, but hunger also may lower discrimination. Again, pilot tests can be run to determine if deprivation affects behavior. Tests are often terminated when 50% of either substrate in a choice trial is consumed. This ensures that apparent discrimination will not be lost if insects entirely consume the preferred substrate, followed by the less-preferred substrate simply due to hunger (Jermy et al. 1968). Water may need to be provided during the test but may not be needed with artificial diets or with turgid leaves. For studies with leaf disks or excised leaves without additional water, it is usually necessary to maintain high humidity, for example, with moistened filter paper lining the test arena to avoid desiccation of leaf material. 

Where substrates are irregularly shaped (e.g., intact leaves) or where the volume consumed cannot be accurately estimated from surface area consumption (e.g., artificial diets), then consumption must be measured by weight loss of the substrate. Weight changes should be on a dry-weight basis, because diets are likely to lose water due to dehydration whether consumed or not during the experiment. 

Food uptake of sucking insects (e.g., aphids and leafhoppers) also is governed by a number of process that occur in several distinct phases. First, the insect 

With sucking insects that produce honeydew, the amount of honeydew excreted is assumed to be proportional to feeding. Honeydew production can be measured as number of droplets (using bromocresol blue or ninhydrin as a stain Auclair 1958), or the stained honeydew can be collected, extracted from the collection chamber, and measured colorimetrically (Nisbet et al. 1994). Several problems must be addressed with the use of honeydew as an index of consumption. First, some aphids will produce nymphs when feeding on artificial diet, and the production of honeydew by nymphs may inflate the quantity recorded for the test insect. The simplest solution here is to frequently remove any nymphs that are produced. Second, because aphids may scatter their honeydew, the droplets will not always fall directly below the aphid. Thus, collection dishes must be sufficiently large to collect all of the honeydew that might be produced. Alternatively, the entire chamber must be lined with material used to collect the honeydew, from which it is extracted subsequently (e.g., Nisbet et al. 1994). 

---

If we are quite certain that ACE immobilized at the surface of the endotheliaf celfs is physiologicaliy more important than is the circulating enzyme (197), we do not know yet what is the relative importance of its bland C-terminal active sites. We do not know how they possibly affect the activity of each other. We do not know the physiological role of the N-acetyl SDKP, a relatively specific substrate of the N-terminal active site. We may still discover other natural substrates for endothelial and epithelial ACE. We do not fully understand the basis of differences in the various daily doses of ACE inhibitors as usually prescribed, from trandolapril 2 mg/day to lisinopril 80 mg/day, and the consequences of dose choices. 

Enzyme-Degradable Hydrogel. Because lysozyme is a well characterized enzyme, our first choice was a lysozyme-degradable hydrogel (11, 12). The natural substrate for lysozyme is chitin (13). but because chitin is a rigid, hydrophobic material, it is clearly not suitable for this work. The other natural substrates for lysozyme are certain bacterial cell-wall peptidoglycans (13. 

If to extend these experiences to the chirality evaluation of linalool from other natural substrates, generally attention must be paid to the GMP-condi-tions as well as to the pH-values of the substrates investigated. 

No other natural substrates have been found for PA. Plasminogen is a component of plasma and also occurs in extravascular spaces. Moreover, since plasmin is a protease with broad substrate specificity and since the amount of circulating plaminogen is relatively high (50 yg/ml), the production of PA may result in extremely high local levels of effective proteolytic activity, due to the amplification achieved by the local conversion of plasminogen to plasmin. 

As in the case of other natural substrates, this novel investigation is aimed at exploiting what one would define as the lower grades of both chitin and chitosan i.e. the by-products resulting from the processing of both materials) compared with the high grade of the refined counterparts. 

Zoutewelle G, Van Wijk R (1990) Effects of Echinacea purpurea extracts on fibroblast populated collagen lattice contraction. Phytotherapy Res 4 77-84 Bos R, Heinzer F, Bauer R (1988) Volatile constituents of the leaves of Echinacea purpurea, E. pallida and E. angustifolia. Poster at the 19. International Symposium on Essential Oils and Other Natural Substrates, 7.-10.9.1988 in Zurich. 

Calixarenes (from the Latin ca/ x) may be understood as artificial receptor analogues of the natural cyclodextrins (96,97). In its prototypical form they feature a macrocycHc metacyclophane framework bearing protonizable hydroxy groups made from condensation of -substituted phenols with formaldehyde (Fig. 15b). Dependent on the ring size, benzene derivatives are the substrates most commonly included into the calix cavity (98), but other interesting substrates such as C q have also been accommodated (Fig. 8c) (45). 

AH 2/3 -dideoxynucleoside analogues are assumed to be intraceUularly phosphorylated to thek active form (5 -triphosphate), and then targeted at the vims-associated reverse transcriptase. The rate and extent of the 2 /3 -dideoxynucleosides phosphorylate to the 5 -triphosphates may be of equal or greater importance than the differences in the relative abiUties of these 5 -triphosphates to inhibit the vkal reverse transcriptase (171). At the level of vkal reverse transcriptase, the 5 -triphosphate of AZT and other dideoxynucleosides may either serve as a competitive inhibitor with respect to the natural substrates or may act as an alternate substrate, thus leading to chain termination (172). 

The [ 2 + 4]-cycloaddition reaction of aldehydes and ketones with 1,3-dienes is a well-established synthetic procedure for the preparation of dihydropyrans which are attractive substrates for the synthesis of carbohydrates and other natural products [2]. Carbonyl compounds are usually of limited reactivity in cycloaddition reactions with dienes, because only electron-deficient carbonyl groups, as in glyoxy-lates, chloral, ketomalonate, 1,2,3-triketones, and related compounds, react with dienes which have electron-donating groups. The use of Lewis acids as catalysts for cycloaddition reactions of carbonyl compounds has, however, led to a new era for this class of reactions in synthetic organic chemistry. In particular, the application of chiral Lewis acid catalysts has provided new opportunities for enantioselec-tive cycloadditions of carbonyl compounds. 

In other cases, new asymmetric centers may be built into the substrate so that the stereochemical course of the overall reaction may be elucidated. The preferred conformation of the natural substrate when bound to the enzyme may be deduced and regions in the space around the enzyme-bound substrate where substituents can be tolerated may be inferred. 

Other inverting glucosidases which conform to the pattern of direct hydrolysis of glycosyl fluorides having the correct anomeric configuration, and transglycosylation with inversion if the anomeric configuration is opposite to that of the natural substrates are trehalase from rabbit renal cortex and from the yeast Candida tropicalis, and ) -D-xylosidase from Bacillus pu-milis. ... 

Halogenation is important for disinfecting drinking water supplies, generally nsing molecular chlorine. Most attention has been directed to the adverse production of haloforms and haloacetates from reactions of chlorine with natural substrates, although in water containing bromide/iodide, a nnmber of other reactions may occur. 

If amylases are to be used as tools for the detailed study of the breakdown and structure of their substrates it is obviously important to separate them from other enzymes and from other naturally associated constituents which may influence the results. It is then equally important to study the properties of the purified amylase and to supply it with the chemical environment necessary to protect it from inactivation and to enable it to act efficiently. With beta amylases this ideal has often been approached. Beta amylases from several sources have been prepared by selective inactivation of other enzymes that accompany them in nature23 and highly active products have been obtained by extensive purification.20 24-26 Balls and his associates have recently reported the crystallization of beta amylase from sweet potato.27... 

BTEX bioremediation projects often focus on overcoming limitations to natural degradative processes associated with the insufficient supply of inorganic nutrients and electron acceptors. However, other limitations associated with the presence and expression of appropriate microbial catabolic capacities may also hinder the effectiveness of bioremediation. Thus, while subsurface addition of oxygen or nitrate has proven sufficient to remove BTEX below detection levels [134,145,292,315,316], it has been only marginally effective at some sites [6]. Sometimes, the concentration of a target BTEX compound fails to decrease below a threshold level even after years of continuous addition of nutrients and electron acceptors [317]. This phenomenon has also been observed for many other xenobiotic and natural substrates under various experimental conditions [327-332]. 

Most of the vanillic acid was reduced by E. coli containing Car in 2 h to vanillin (80 %) and vanillyl alcohol (20 %). Car does not reduce aldehydes to alcohols. However, E. coli s endogenous aldehyde reductase/dehydrogenase reduces vanillin to vanillyl alcohol. The broad substrate specificity of Car enables the wide application of this biocatalyst to other important applications, such as enantiomeric resolution of isomers such as ibuprofen and the reductions of many other natural and synthetic carboxylic acids. 

Two compounds other than the natural substrate SAM, l-VG and S -methyl-L-methionine (SMM), have been described so far as both substrates and inhibitors of ACS isozymes. l-VG was isolated 30 years ago from the fungus Rhodophyllus nidorosus It was shown to be a mechanism-based inhibitor of aspartate aminotransferase and kynurenine aminotransferase. First of all, l-VG is an alternative substrate of ACS in addition to being an inhibitor as described in the previous section. ... 

---