Feedback-regulated

In this scheme, F symbolizes an essential metabolite, such as an amino acid or a nucleotide. In such systems, F, the essential end product, inhibits enzyme 1, xAie first step in the pathway. Therefore, when sufficient F is synthesized, it blocks further synthesis of itself. This phenomenon is called feedback inhibition or feedback regulation. 

Enzymes such as enzyme 1, which are subject to feedback regulation, represent a distinct class of enzymes, the regulatory enzymes. As a class, these enzymes have certain exceptional properties ... 

Production of phenylalanine starts after depletion of tyrosine at about 6 hours. This is logical since the micro-oiganism needs a certain amount of tyrosine, for example to synthesise key enzymes, but synthesis of L-phenylalanine is feedback regulated if tyrosine is present. 

FEEDBACK REGULATION IS NOT SYNONYMOUS WITH FEEDBACK INHIBITION... 

Regulation of the erythroid form of ALAS (ALAS2) differs from that of ALASl. For instance, it is not induced by the drugs that affect ALASl, and it does not undergo feedback regulation by heme. 

Figure 34-6. Regulation of the reduction of purine and pyrimidine ribonucleotides to their respective 2 -deoxyribonucleotides. Solid lines represent chemical flow. Broken lines show negative ( ) or positive ( ) feedback regulation.

QUESTION Do you think that there is a similar feedback regulation system of the reticulata part for the nigra ... 

Bachmann, H., A. Desbarats et al. (2002). Feedback regulation of beta,beta-carotene 15,15 -monooxygenase by retinoic acid in rats and chickens. J. Nutr. 132(12) 3616-3622. 

Bennett MK, Lopez JM, Sanchez HB, Osborne TF. Sterol regulation of fatty acid synthase promoter. Coordinate feedback regulation of two major lipid pathways. J Biol Chem 1995 270 25578-25583. 

The major FSH target in the male is the Sertoli cells, found in the walls of the seminiferous tubules of the testis. They function to anchor and nourish the spermatids, which subsequently are transformed into spermatozoa during the process of spermatogenesis. Sertoli cells also produce inhibin (discussed later), which functions as a negative feedback regulator of FSH. The major physiological effect of FSH in the male is thus sperm cell production. 

Serizawa, S. et al. Negative feedback regulation ensures the one receptor-one olfactory neuron rule in mouse. Science 302 2088-2094,2003. 

Estrogen Feedback Regulation of Hypothalamus-Pituitary Axis... 

Based on a previously constructed model, two crucial questions with respect to dynamic properties were investigated [296] (i) What is the role of feedback regulation in maintaining the stability of the steady state. In particular, does the feedback regulation contribute to a stabilization of the in vivo metabolic state (ii) Is it possible to distinguish between different metabolic states That is, does knowledge of the metabolic state, characterized by the flux distribution and metabolite concentrations, indeed constrain the dynamic properties of the system ... 

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