Synthesis of, enzymes

Microorganisms exhibit nutritional preferences. The enzymes for common substrates such as glucose are usually constitutive, as are the enzymes for common or essential metabohc pathways. Furthermore, the synthesis of enzymes for attack on less common substrates such as lactose is repressed by the presence of appreciable amounts of common substrates or metabolites. This is logical for cells to consei ve their resources for enzyme synthesis as long as their usual substrates are readily available. If presented with mixed substrates, those that are in the main metabolic pathways are consumed first, while the other substrates are consumed later after the common substrates are depleted. This results in diauxic behavior. A diauxic growth cui ve exhibits an intermediate growth plateau while the enzymes needed for the uncommon substrates are synthesized (see Fig. 24-2). There may also be preferences for the less common substrates such that a mixture shows a sequence of each being exhausted before the start of metabolism of the next. 

More than 30 years ago Jacob and Monod introduced the Escherichia coli lac operon as a model for gene regulation. The lac repressor molecule functions as a switch, regulated by inducer molecules, which controls the synthesis of enzymes necessary for E. coli to use lactose as an energy source. In the absence of lactose the repressor binds tightly to the operator DNA preventing the synthesis of these enzymes. Conversely when lactose is present, the repressor dissociates from the operator, allowing transcription of the operon. 

Tatsumi, H., Masuda, T., and Nakano, E. (1988). Synthesis of enzymically active firefly luciferase in yeast. Agric. Biol. Chem. 52 1123-1127. 

Suggest a synthesis for (76) needed for the synthesis of enzyme inhibitors. 

Metabolic pathways are regulated by rapid mechanisms affecting the activity of existing enzymes, eg, allosteric and covalent modification (often in response to hormone action) and slow mechanisms affecting the synthesis of enzymes. 

Long-chain fatty acid synthesis is controlled in the short term by allosteric and covalent modification of euTymes and in the long term by changes in gene expression governing rates of synthesis of enzymes. 

Hegeman GD (1966) Synthesis of the enzymes of the mandelate pathway by Pseudomonas putida I synthesis of enzymes of the wild type. J Bacteriol 91 1140-1154. 

It is well known that chemical compo.sition of rhizosphere solution can affect plant growth. Particularly, uptake of nutrients may be considerably influenced by the ionic concentration of the rhizosphere solution (40). Despite the difficulty of defining the exact concentration of ions in the rhizosphere surrounding each root (or even root portion), it has been unequivocally demonstrated that plants have evolved mechanisms to cope with the uneven distribution of ions in the root surrounding in order to provide adequate supply of each essential nutrient (41). These mechanisms include expression of transporter genes in specific root zones or cells and synthesis of enzymes involved in the uptake and assimilation of nutrients (40,43). Interestingly, it has been shown that specific isoforms of the H -ATPase are expressed in the plasma membrane of cell roots it has been proposed that the expression of specific isoforms in specific tissues is relevant to nutrient (nitrate) acquisition (44) and salt tolerance (45). 

Design and Synthesis of Enzyme Mimics of P-Carotene 15,15 -monooxygenase 35... 

Toxi-ChromoPad (EBPI, Ontario, Canada) is a simple method for evaluation of the toxicity of solid particles [25,26,32,39]. The test is based on the inhibition of the synthesis of (3-galactosidase in E. coli after exposure to pollutants. The method has been used to measure acute toxicity of sediment and soil and other solid samples. The test bacterial suspension is mixed with homogenized samples and incubated for 2 hours. A drop of the test solution is pipetted onto a fiberglass filter containing an adsorbed substrate. A color reaction indicates the synthesis of enzyme, while a colorless reaction indicates toxicity. It has previously been shown... 

Figure 1. Schematic of synthesis of enzyme immobilized within hydrogel exhibiting thermally reversible shrinking and swelling.

Saccharidic Difluorophosphonates Difluoromethylene phospho-nates have been the focus of numerous works. Indeed, these compounds are able to mimic the phosphate bond in the synthesis of enzyme inhibitors. This interest is obvious for the furanose series in this case, they are non scissible analogues of 5-phosphate nucleosides (cf. Chapter 7). Difluoromethylene phosphonates can be prepared via a radical path starting from compounds that have the difluoromethylene moiety in the pseudo-anomeric position. Nevertheless, methods based on metal derivatives of difluorophosphonates are generally easier and broadly applicable. 

It is more difficult to prepare a chiral a,a-dialkylammo acid. Nevertheless, when such analogues are incorporated into the backbone of a peptide chain, analogues with modified properties are obtained. In this context, such residues have been evaluated as a new type of conformational constraint for the synthesis of enzyme-resistant agonists and antagonists of bioactive peptides. Here, the asymmetric synthesis or the resolution of the chiral quaternary amino acid is necessary and numerous procedures, which have recently been reviewed, were developed to produce the requisite amino acids in enantiomerically pure form. 

I believe that the bottom-up approach to the origin of life will enjoy a considerable boost, when conditions are found for the prebiotic synthesis of many identical copies of long (>30) co-oligopeptide or co-oligonucleotide sequences. This would at least show that the prebiotic synthesis of enzymes and/or RNA is in principle possible. This remains the main problem with the prebiotic RNA world. 

Most of the established pharmacological effects of glucocorticoids are mediated by cytoplasmic glucocorticoid receptors. After binding to the receptor, the steroid-receptor complex binds to chromatin and stimulate the formation of mRNA. The mRNA stimulates the synthesis of enzymes which produce various pharmacological actions. 

Induction involves increased synthesis of enzyme protein, which may be detected as an increase in total enzyme level as with phenobarbital induction or increase in a particular isoenzyme. Protein synthesis is increased, and this usually seems to be necessary as inhibition of protein synthesis results in inhibition of induction. The increased protein synthesis may involve increased mRNA synthesis and inhibitors of this, such as actinomycin D, block induction. For a simple diagram explaining the relationship of protein synthesis to DNA see Figure 6.38. 

Reduced synthesis. The synthesis of enzymes may be decreased, resulting in a decrease in the in vivo activity. With cytochrome P-450 there are a number of ways in which this occurs. Thus, administration of the metal cobalt to animals will decrease levels of cytochromes P-450 by inhibiting both the synthesis and increasing the degradation of the enzyme. Thus, cobalt inhibits S-aminolaevulinic acid synthetase, the enzyme involved in heme synthesis. Cobalt will also increase the activity of heme oxygenase, which breaks down the heme portion to biliverdin. The compound 3-amino, 1, 2, 3-triazole decreases cytochromes P-450 levels by inhibiting porphyrin synthesis. 

V. L. Yarovenko Theory and Practice of Continuous Cultivation of Microorganisms in Industrial Alcoholic Processes. - Y. Miura Mechanism of Liquid Hydrocarbon Uptake by Microorganisms and Growth Kinetics. -J. E. Zajic, N. Kosaric, J. D. Brosseau Microbial Production of Hydrogen. - T.Enatsu, AShin-myo In vitro Synthesis of Enzymes. Physiological Aspects of Microbial Enzyme Production. 

Cells also regulate the synthesis of their own catalysts, the enzymes, in response to increased or diminished need for a metabolic product this is the substance of Chapter 28. The expression of genes (the translation of information in DNA to active protein in the cell) and synthesis of enzymes are other layers of metabolic control in the cell. All layers must be taken into account when describing the overall control of cellular metabolism. Assembling the complete picture of how the cell regulates itself is a huge job that has only just begun. 

FIGURE 12-43 Variations in the activities of specific CDKs during the cell cycle in animals. Cyclin E-CDK2 activity peaks near the G1 phase-S phase boundary, when the active enzyme triggers synthesis of enzymes required for DNA synthesis (see Fig. 12-46). Cyclin A-CDK2 activity rises during the S and G2 phases, then drops sharply in the M phase, as cyclin B-CDK1 peaks. 

To meet these changing circumstances, the liver has remarkable metabolic flexibility. For example, when the diet is rich in protein, hepatocytes supply themselves with high levels of enzymes for amino acid catabolism and gluconeogenesis. Within hours after a shift to a high-carbohydrate diet, the levels of these enzymes begin to drop and the hepatocytes increase their synthesis of enzymes essential to carbohydrate metabolism and fat synthesis. Liver enzymes turn over (are synthesized and degraded) at live to ten times the rate of enzyme turnover in other tissues, such as muscle. Extrahepatic... 

Genetic factors influence the rate of not only synthesis of proteins but also their breakdown, i.e., the rate of turnover. As we have seen in Chapter 10, some enzymes are synthesized as inactive proenzymes which are later modified to active forms, and active enzymes are destroyed, both by accident and via deliberate hydrolytic pathways. Protein antienzymes may not only inhibit enzymes but may promote their breakdown.35 An example is the antienzyme that controls ornithine decarboxylase, a key enzyme in the synthesis of the polyamines that are essential to growth.36,37 As with all cell constituents, the synthesis of enzymes and other proteins is balanced by degradation. 

Peptides - [ANTIBIOTICS - PEPTIDES] (Vol 3) - [TRACE AND RESIDUE ANALYSIS] (Vol 24) -m beer [BEER] (Vol 4) -as endogenous opioids [OPIOIDS, ENDOGENOUS] (Vol 17) -enzymatic synthesis of [ENZYMES IN ORGANIC SYNTHESIS] (Vol 9) -radiolabeling of [RADIOPHARMACEUTICALS] (Vol20)... 

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