Enzymes holoenzyme

Coenzyme An organic nonprotein molecule, frequently a phosphorylated derivative of a water-soluble vitamin, that binds with the protein molecule (apoenzyme) to form the active enzyme (holoenzyme). [EU]... 

Organism/ enzyme Holoenzyme Mr (kDa) Subunits/Mr(kDa) W content FeS or cluster contenC Pterin co factor d... 

A complete catalytically active enzyme together with its coenzyme and/ or metal ions called a holoenzyme. Apo-enzyme + Co enzyme == Holoenzyme. 

Enzymes (holoenzymes) consist of two main parts - a pure protein part (apo- enzyme), and a non-protein part (cofactor) Holoenzyme = Apoenzyme -i- Cofactor. 

Basically, the plant RIPs can be subdivided into holoenzymes and chimero-enzymes. Holoenzymes or type 1 RIPs consist solely of a RIP domain, whereas the chimero-enzymes are built up of an N-terminal RIP domain linked (at least in the gene) to an unrelated C-terminal domain. Depending on the nature of the latter chain, the chimeric forms are referred to as type II RIPs (with a lectinic B-chain) and type IB RIPs (with an unidentified C-terminal domain). Both type I and type II RIPs are quite common in plants whereas hitherto only a single type III RIP has been isolated and characterized, namely the barley JIP60 [27]. 

The two subunits of CODH/ACS have been dissociated to offer a clearer picture of the ACS active site 135). The holoenzyme contains 2 Ni, 12 Fe, and 14 S 120) that are organized into 3 discrete clusters, whereas the isolated a subunit contains only 1 Ni and 4 Fe and has spectroscopic properties similar to those of Cluster A in the native enzyme 186). Based on EXAFS spectroscopy of the a. subunit, the Ni site in Cluster A has been proposed to be coordinated to 2 sulfur ligands at 2.19 A and 2 nitrogen or oxygen ligands at 1.89 A in a distorted square plane 186). 

GGPPS functions as part of a complex metabolon. In the plastid, as shown in Capsicum chromoplasts," GGPPS is a homodimer and associated but not integral to the plastid envelope. GGPPS is also associated with the next enzyme in the pathway as part of a holoenzyme complex." " ... 

A homogeneous electrochemical enzyme immunoassay for 2,4-dinitrophenol-aminocaproic acid (DNP-ACA), has been developed based on antibody inhibition of enzyme conversion from the apo- to the holo- form Apoglucose oxidase was used as the enzyme label. This enzyme is inactive until binding of flavin adenine dinucleotide (FAD) to form the holoenzyme which is active. Hydrogen peroxide is the enzymatic product which is detected electrochemically. Because antibody bound apoenzyme cannot bind FAD, the production of HjOj is a measure of the concentration of free DNP-ACA in the sample. 

Type III-PHA synthase is represented by the enzyme of Chromatium vino-sum and is encoded by phaECCv. It consists of the two different subunits PhaCCv and PhaECv exhibiting molecular weights of 39,730 and 40,525 Da, respectively [23]. The native PHA synthase, as isolated from recombinant strains of E. coli, exhibited a molecular weight of approximately 390 and 400 + 20 kDa as revealed in our laboratory [54] or 360 + 50 kDa but also 520 + 50 kDa as revealed in another laboratory [55]. The lower molecular weights for the holoenzyme are... 

Enzymes may not function well or at all unless some other species known as a cofactor is present. An enzyme alone is referred to as the apoenzyme and the combination of enzyme and cofactor is known as the holoenzyme. Among the species that function as cofactors are organic compounds that interact with the enzyme. If the organic moiety is strongly attached to the enzyme, it is called a prosthetic group, but if it is loosely bound to the enzyme, it is referred to as a coenzyme. For the purposes of this discussion, the most interesting cofactors are metal ions. Depending on the type of enzyme, the appropriate metal ion cofactor may be Mg2+, Ca2+, K+, Fe2+, or Cu2+. A sizeable number of enzymes are sometimes called metalloenzymes because they have active sites that contain a metal. 

TN was increased by the presence of the general acid. These observations suggested that H2O serves to donate the protons required to form product H2O2. Values of Km and TN for the zinc-deficient enzyme were found to be approximately a factor of two less than those obtained for the holoenzyme under identical experimental conditions, whereas TN/Xm was largely unchanged. The authors concluded that the imidazolate bridge is thus not essential for catalytically competent extraction of a proton from the solvent by CuZnSOD. 

Core extrusion studies—removal of the iron-sulfur cluster intact from the enzyme surroundings—have been carried out and the iron-cluster types in proteins identified through the process shown in equation 6.10.18 DMS0/H20 is the protein unfolding solvent for this process. By this method, Fe-protein and MoFe-protein metal-sulfur clusters have been removed from the holoenzyme for separate analysis by many instrumental techniques. 

Although the first purification of bNOS was a monomer, it is now clear that the enzyme in all cases is effective as a dimer. A purified macrophage iNOS was used by Baek and coworkers98 to separate the holoenzyme from the monomers. The subunits do not have NOS activity but do have the ability to oxidize reduced triphosphopyridine nucleotide with either ferricyanide, cytochrome c or dichlorophenolindophenol. When all of the missing factors are present, but not when any is missing, the authors find recombination, as shown in Figure 13. 

Although the matter cannot be regarded as completely settled, it seems likely that during the oxidase reaction a His/Met ferric c heme occurs. This might be expected to be more readily reduced by ascorbate than the His/His form, thus explaining the more rapid reduction of the enzyme by ascorbate after an initial oxidation by oxygen. Support for this view comes from the finding that the semi-apo enzyme is much more rapidly reduced by ascorbate than the as prepared oxidized holoenzyme. 

It has been suggested that the inhibition of ALDH by AGP 17 starts with an interaction between the amino group of 17 and the cysteinyl thiolate side chain of the enzyme to form a modified holoenzyme, or that the enzymic reaction may either proceed through the cyclopropanone 20 yielding 24 a or through the imi-nium ion 18, yielding the modified enzyme 24b [17]. Thus, the covalent he-mithioacetal 24a or hemithioaminal enzyme derivatives 24b rapidly accumulate in the enzyme microenvironment and lead to the observed activity loss, Eq. (9) [21]. 

The RNA polymerase of E. coli possesses with its subimit construction (a2PP o) a simple structure in comparison to eucaryotic RNA polymerases. The sigma factor is only required for the recognition of the promoter and the subsequent formation of a tight complex. After the incorporation of the first 8-10 nucleotides into the transcript, the sigma factor dissociates from the holoenzyme, and the remaining core enzyme carries out the rest of the elongation. 

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