Protein-enzyme complexes

Lilly 1977). For the conversion of benzene to DHCD, the intact cell as a catalyst is preferred for several reasons. First, the reaction requires NADH, which can be supplied by the cell. Second, appropriate host strains have been supplied by strain development which are resistant to toxic organic substrates and can take up a range of aromatic compounds. Moreover, for the option of using dissolved enzymes as synthetic catalysts, it has been unsuccessful in isolating the three-protein enzyme complex (Yeh et al. 1977 Axcell and Geary 1975 Zamanian and Mason 1987 Mason and Cammack 1992). 

Multi-Protein Enzyme Complexes in the Ubiquinone Pathway... 

Plants usually obtain their nitrogen by absorption of nitrate or ammonium ions from the soil (symbiotic associations between higher plants and nitrogen fixing bacteria are of course exceptions to this). Ammonium ions may be utilized directly in the synthesis of amino acids (see p. 169), but nitrate must first be reduced to ammonia. This is accomplished in two stages the reduction of nitrate to nitrite followed by the reduction of nitrite to ammonia. The first step— nitrate reduction—is catalysed by the flavo-protein enzyme complex nitrate reductase (Fig. 5.12) which contains molybdenum and FAD (flavin adenine dinucleotide) as a prosthetic group. Reduced FMN... 

Proteins are complex molecules that give cells structure and act as both enzymes and motors within cells. Proteins are long strings of amino acids folded in specific three-dimensional formations. There are twenty different animo acids in our bodies. DNA, the genetic material located in the cell nucleus, carries information for the order of the amino acids in each protein. Indeed, in the simplest sense, a gene is the... 

When induced in macrophages, iNOS produces large amounts of NO which represents a major cytotoxic principle of those cells. Due to its affinity to protein-bound iron, NO can inhibit a number of key enzymes that contain iron in their catalytic centers. These include ribonucleotide reductase (rate-limiting in DNA replication), iron-sulfur cluster-dependent enzymes (complex I and II) involved in mitochondrial electron transport and cis-aconitase in the citric acid cycle. In addition, higher concentrations of NO,... 

In general, the receptor-G-proteins complexes exchange bound GDP for GTP. In turn, the two, smaller subunits of the G-protein components of these complexes are released and the receptor protein dissociates. The remaining G-protein GTP complex then complexes with and activates a specific enzyme. It is very significant to note that G-proteins therefore have at least three specific binding sites (a) for nucleotides, (b) for a receptor protein, and (c) an effector protein. 

Since the pioneering work of Kleymann et al. (2002), Betz et al. (2002), Baumeister et al. (2007), and Crute et al. (2002), who showed that compounds identified as inhibitors of the helicase-primase enzyme complex could alleviate herpesvirus-induced disease in animal models, the attention of researchers developing antiviral compounds has been drawn more and more towards the virus-encoded helicases, particularly those of Herpes viruses and of RNA viruses such as Hepatitis C Virus (HCV) and SAKS coronavirus (SARS-CoV). Enzyme activity is usually assayed by measuring NTPase activity in the presence of an appropriate nucleic acid co-substrate although, more recently, novel fiuorimetric and luminescence principles have been applied to the measurement of strand unwinding and/or translocation of the protein along the nucleic acid (Frick 2003, 2006). 

It is becoming clear that the MgATP hydrolysis is not required to induce protein-protein electron transfer, but its role in nitrogenase function is still undefined. The most likely hypothesis at the moment is that its hydrolysis, on the Fe protein, induces important changes in the MoFe protein, presumably by altering the conformation of the enzyme complex. Nevertheless, the nature of the changes in the MoFe protein remain obscure. 

Cellulase enzyme complexes consist of three major types of proteins that synergistically catalyze the breakdown of a cellulosic substrate. Because the enzymes are strictly substrate-specific in their action, any change in the structure or accessibility of the substrate can have a considerable influence on the course of the hydrolysis reaction. A pretreatment method based on exposing cellulosic substrate to phosphoric acid solution [9] and addition of the nonionic... 

Proteosome An enzyme complex that degrades intracellular proteins. 

Adenosine deaminase (ADA) is an amino hydrolase that catalyzes the deamination of adenosine and 2 -deoxyadenosine to inosine and 2 -deoxyinosine, respectively. High activity of ADA is seen in thymus and other lymphoid tissues. ADA has been shown in many different physical forms. A small form of the enzyme predominates in the spleen, stomach, and red blood cells, whereas the large form predominates in the kidney, liver, and skin fibroblasts. The small form of the catalytic subunit can be converted to the large form by complexing with a protein termed binding protein or complexing protein. 

The FePcY-PDMS supramolecular catalyst resembles the architecture of natural enzymes. In this system the PDMS membrane takes over the role of the phospholipid double layer likewise, the zeolite imitates the protein and the FePc complex the Fe-protoporphyrin. Zeolite-encaged Cu-histidine complexes were also studied as mimics of natural Cu-enzyme complexes.173... 

A hypercycle is a more complex organisation form. Its precondition is the presence of several RNA quasi-species which are able to amalgamate chemically with certain proteins (enzymes or their precursors). If such a protein is linked to a quasi-species, the resulting duo favours the replication of a second quasispecies. According to Dyson, the linked populations get stuck in a stable equilibrium. Problems occur at this level Any theory on the origin of replication has the central problem that the replication process must occur perfectly in order to ensure survival . If there are replication errors, these will increase from generation to generation, until the system collapses the error catastrophe has then occurred ... 

The hypercycle models developed later by Eigen were much more complex. Since both protein enzymes and nucleic acids contribute to hypercycles, the latter could only have come into operation at a later stage of the (hypothetical) RNA world. It seems possible that the protein enzymes on the primeval Earth could have been replaced by ribozymes. 

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