Proteins energy conversions catalyzed

Electron-transfer (ET) reactions play a central role in all biological systems ranging from energy conversion processes (e.g., photosynthesis and respiration) to the wide diversity of chemical transformations catalyzed by different enzymes (1). In the former, cascades of electron transport take place in the cells where multicentered macromolecules are found, often residing in membranes. The active centers of these proteins often contain transition metal ions [e.g., iron, molybdenum, manganese, and copper ions] or cofactors as nicotinamide adenine dinucleotide (NAD) and flavins. The question of evolutionary selection of specific structural elements in proteins performing ET processes is still a topic of considerable interest and discussion. Moreover, one key question is whether such stmctural elements are simply of physical nature (e.g., separation distance between redox partners) or of chemical nature (i.e., providing ET pathways that may enhance or reduce reaction rates). 

The chosen three examples result from our newly developed understanding of protein-catalyzed energy conversion. This brings us to the modern-day situation so well-stated by J. Bronowski, In effect, the modem problem is no longer to design a structure from the materials, but to design the materials for a stmeture. ... 

Changes in Folding and Association of Oil-like Domains of Protein Chains Give Rise to Protein-catalyzed Energy Conversion... 

The position of the T,-divide that separates soluble from insoluble (hydrophobically associated) states in the phase diagram depends on seven variables on the six intensive variables of temperature, chemical potential, electrochemical potential, mechanical force, pressure, and electromagnetic radiation, and on polymer volume fraction or concentration. Therefore, diverse protein-catalyzed energy conversions by the consilient mechanism result from designs that control the location of the Tfdivide in this seven-dimensional phase transitional space. Complete mathematical description has yet to be written for representation of the T,-divide in seven-dimensional phase transitional space, but it may prove to be more relevant to... 

Another example is the Principle of Le ChStelier, which may be stated as follows For any system at rest (at equilibrium) the introduction of a stress (in our case an input energy) causes the system to react in such a way as to relieve the stress (in our case by an output energy). This principle reasonably describes protein-catalyzed energy conversion, that is, the function of protein-based machines. Under prescribed conditions, properly designed model protein-based machines exhibit a behavior where for each action there is a reaction. In section 5.4, regardless of the action, which was any one of several different input energies, the performance of mechanical work was the reac-... 

Eight enzyme-catalyzed reactions are involved in the conversion of acetyl-CoA into fatty acids. The first reaction is catalyzed by acetyl-CoA carboxylase and requires ATP. This is the reaction that supplies the energy that drives the biosynthesis of fatty acids. The properties of acetyl-CoA carboxylase are similar to those of pyruvate carboxylase, which is important in the gluconeogenesis pathway (see chapter 12). Both enzymes contain the coenzyme biotin covalently linked to a lysine residue of the protein via its e-amino group. In the last section of this chapter we show that the activity of acetyl-CoA carboxylase plays an important role in the control of fatty acid biosynthesis in animals. Regulation of the first enzyme in a biosynthetic pathway is a strategy widely used in metabolism. 

The creatine synthesized in the liver is transported through the bloodstream to skeletal and heart muscle. It enters the mitochondria, where it is phosphorylated to crealine-P Creatine kinase catalyzes this reversible addition of a phosphate group, as shown in Figure 4.34. Creatine-P is unique in that its only known function is as an energy buffer. The creatine P formed in the mitochondria travels to the contractile proteins in the cytoplasm of the muscle fiber. The polymer, or complex, of contractile proteins is called a myofibril. Contraction of a myofibril is coupled to the hydrolysis of ATP to ADP. The immediate replenishment of ATP is catalyzed by a second creatine kinase, residing on the myofibril, that catalyzes the conversion of creatine-P to creatine. This reversal of the reaction takes place in the... 

Fig. 9. Reciprocal regulation of fatty acid synthesis and oxidation. Malonyl-CoA, the product of the ACC reaction, inhibits CPT-1, which is localized at the outer mitochondrial membrane and catalyzes the conversion of fatty acyl-CoA to fatty acyl-camitine for mitochondrial fatty acid import and oxidation. At the inner mitochondrial membrane, fatty acyl moieties are converted to CoA thioesters by CPT-II before undergoing -oxidation. ACC is activated by citrate and inhibited by fatty acyl-CoA. AMPK is activated by AMP and the high AMP level reflects the low energy state of the cell. Activation of AMPK in response to increases in AMP involves phosphorylation by an upstream AMPK kinase (AMPKK), the tumor suppressor LKB1, and AMPK is inactivated/dephosphory-lated by protein phosphatase 2A (PP2A), which is first activated by insulin via PI3K/Akt pathway. ACC is dephosphorylated/activated by PP2A and is inactivated upon phosphorylation by AMPK. ACC can also be phos-phorylated/inactivated by PKA. TAG, triacylglycerol FA, fatty acid.

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