Regulation of synthesis

Dopamine (DA) and norepinephrine (NE) are allosteric inhibitors of tyrosine hydroxylase and regulate catecholamine synthesis when the adrenal medulla is quiescent (unstimulated). Continuous stimulation of the adrenal medulla (as during prolonged stress) promotes tyrosine hydroxylase activity primarily because the turnover of DA and NE is rapid. Tyrosine hydroxylase activity is also regulated by cAMP and by cholinergic nerve activity. The enzyme is active when phos-phorylated (Chapter 30). Tonic cholinergic impulses maintain the activity of tyrosine hydroxylase, whereas 

Synthesis and metabolism of catecholamines. Arrows indicate molecular conversions catalyzed by specific enzymes. Bold arrows indicate major (preferred) pathways. Enzymes (I) tyrosine hydroxylase (2) aromatic L-amino acid decarboxylase (3) dopamine-jSymonooxygenase (4) PNMT (5) cateckel-o-methyltransferase (6) monoamine oxidase. 

Epinephrine production is catalyzed by PNMT, which is induced by glucocorticoids (cortisol). The venous drainage of the adrenal cortex, which contains very high concentrations of newly released cortisol, bathes the adrenal medulla before entering the general circulation. 

---

A summary of some of these processes is as follows synthesis of phospholipids and cholesterol de novo synthesis of ribonucleotides synthesis of RNA de novo synthesis of deoxyribonucleotides regulation of synthesis of deoxyribonucleotides salvage pathways duplication of DNA transcription and translation (polypeptide synthesis). After this series of topics, those of fuels and ATP generation, mitosis and, finally, regulation of the cycle, are described and discussed. 

Regulation of Synthesis and Accumulation of Proteinase Inhibitors in Leaves of Wounded Tomato Plants... 

Comeau, D.E. Ikenaka, K. Tsung, K.L. Inouye, M. Primary characterization of the protein products of the Escherichia coli ompB locus structure and regulation of synthesis of the OmpR and EnvZ proteins. J. Bacteriol., 164, 578-584 (1985)... 

Anti-glycosyl antibodies isolated from the sera of some animals immunized with bacterial carbohydrate antigens are of a restricted heterogeneity, that is, they occur in relatively few, multimolecular forms.145 146 Such antibodies have been used in studies on the structure of antibodies,147 and on the genetic regulation of synthesis of anti-... 

The regulatory mechanisms described above modify the activity of existing enzyme molecules. However, cells can also regulate the amount of enzyme present—usually by altering the rate of enzyme synthesis. The increased (induction) or decreased (repression) of enzyme synthesis leads to an alteration in the total population of active sites. [Note The efficiency of existing enzyme molecules is not affected.] Enzymes subject to regulation of synthesis are often those that are needed at only one stage of development or under selected... 

Most proteins in the body are constantly being synthesized and then degraded, permitting the removal of abnormal or unneeded proteins. For many proteins, regulation of synthesis determines the concentration of protein in the cell, with protein degradation assuming a minor role. For other proteins, the rate of synthesis is constitutive, that is, relatively constant, and cellular levels of the protein ae controlled by selective degradation. 

Gupta, S.C. Beevers, L. (1985). Regulation of synthesis of nitrate reductase in pea leaves in-vivo and in-vitro studies. Planta 166,89-95. 

A final point concerning regulation of synthesis of hsp s concerns the fact that activities of chaperones often reflect a cooperative effort that involves two or more chaperones working in concert. Thus, more than one chaperone may... 

Regulation of synthesis Thyroid function is controlled by a tropic hormone, thyroid-stimulating hormone (TSH, thyrotropin), a glycoprotein synthesized by the anterior pituitary (see Figure 25.2). TSH generation is governed by the hypothalamic thyrotropin-... 

Regulation of Synthesis and Degradation of Copper Homeostasis Machinery... 

A striking feature of neurotransmitter ch istry is the precise regulation of synthesis, that, for example, results in a few neurons synthesizing a particular neuropeptide while all the rest do not. It appears from the vertebrate literature that mature neurons also precisely regulate the rate of neuropeptide synthesis... 

---