Oligomeric enzymes

Ni, but it had the native enzyme oligomeric organization (46). Thus, the C-terminal extension is needed for Ni incorporation, which, in turn, is not needed for subunit assembly. 

It is impossible to describe and explain enzyme kinetics unless is explained by an entire book therefore, this chapter describes only briefly some aspects. It is strongly recommended to read once more a textbook on enzymology and enzyme kinetics. Especially the reaction kinetics of enzyme oligomeres, multi-enzyme complexes, and phenomena of cooperation are too complex to explain in just a few pages. 

A distinctly different form of acetyl-CoA carboxylase is found in the cytosol of animal tissues. The rat liver enzyme is a dimer composed of two identical subunits (Mr of each = 265,000) with one biotin per subunit. In contrast to the multienzyme complex in E. coli, the three functional parts of acetyl-CoA carboxylase in rat liver occur in a single multifunctional polypeptide. The enzyme, as a dimer, has very low activity. However, in the presence of citrate the enzyme oligomerizes to an active form, a polymer with a... 

Still, there seems to be something to this surface-to-volume ratio idea, because a number of normally monomeric enzymes oligomerize when they are found in hyperthermophilic organisms. Adenylate kinase from S. acidocaldarius is a trimer, for example, whereas nearly all other adenylate kinases are monomeric. Perhaps the best evidence that this effect may be important comes from an engineered protein, the repressor of primer (ROP). ROP is normally an all helical homod-imeric protein that denatures at 71°. Removal of five amino acids from a surface... 

Cold-sunsitivu enzymes oligomeric enzymes which show decreased stability and loss of enzymatic activity with decreasing temperature. Low temperature causes these enzymes (about 25 are known) to dissociate into inactive subunits, due to weakening of... 

Enzyme Oligomeric enzyme molecules Subunits per enzyme molecule Total subunits... 

Matthews, B.W., Bernhard, 5.A. Structure and symmetry of oligomeric enzymes. Annu. Rev. Biophys. Bioeng. 

Many enzymes (see Chapters 14 to 16) derive at least some of their catalytic power from oligomeric associations of monomer subunits. This can happen in several ways. The monomer may not constitute a complete enzyme active site. Formation of the oligomer may bring ail the necessary catalytic groups together to form an active enzyme. For example, the active sites of bacterial glutamine synthetase are formed from pairs of adjacent subunits. The dissociated monomers are inactive. 

Oligomeric enzymes may also carry out different but related reactions on different subunits. Thus, tryptophan synthase is a tetramer consisting of pairs of different subunits, Purified a-subunits catalyze the following reaction ... 

Allosteric enzymes have an oligomeric organization. They are composed of more than one polypeptide chain (subunit) and have more than one S-bind-ing site per enzyme molecule. 

Most enzymes consist of several identical or different subunits. It is known that subunits of similar activity but different origin, which therefore differ in size and amino acid composition and sequence, replace each other in oligomeric enzymes, leading to the formation of enzyme chimeras of catalytic activity 47). The feasibility... 

Bonk, M. et al., Chloroplast import of four carotenoid biosynthetic enzymes in vitro reveals differential fates prior to membrane binding and oligomeric assembly, Eur. J. Biochem. 247, 942, 1997. 

HPAEC analyses were carried out to determine the oligomeric products released from various pectic substrates after depolymerization by the PL isoenzymes. Action pattern analyses for the concerted action of PL isoenzymes utilized 68% esterified pectin as substrate. One-ml reaction mixtures in a buffer system as detailed in section 2.2. comprising 0.5% (w/v) substrate and 5 U of enzyme were incubated for 30 s to 18 h, and then thermoinactivated. Samples of 750 pi were applied to a Carbopac PA-1 (Dionex) column before the carbohydrates were eluted over a period of 70 min using a gradient of 0.2 M KOH, 0.05 M K-acetate to 0.2 M KOH, 0.7 M K-acetate. Detection employed a Pulsed Electrochemical Detector (PED, Dionex) in the integrated amperometry mode according to the manufacturer s recommendations. 

BACE-1 (p-secretase) is one of the enzymes involved in breaking down APP to produce Ap (amyloid p-peptide, Ap40>42), the protein that eventually oligomerizes to form Ap plaques, the hallmark of Alzheimer s disease (AD). Thus an agent that... 

The first products of enzymatic hydrolysis of poly(3HB) by purified poly(3HB) depolymerases are a mixture of monomeric and/or oligomeric 3-hydroxybuty-rate esters. Some enzymes are able to hydrolyze oligomers and dimers to monomeric 3-hydroxybutyrate after prolonged time of hydrolysis in the presence of an excess of the appropriate depolymerase. These poly(3HB) depolymerases have high endogenous dimer-hydrolase activities (e.g., the poly(3HB) depolymerases of Comamonas strains, P. stutzeri, S. exfoliatus, and the depolymerases... 

The fungal transformation of estrogens, by enzymes or cells, seems to produce metabolites with reduced estrogenic activity in short periods, usually days or even few hours. However, only oligomeric products have been identified in enzymatic processes and a lack in the identification of metabolites derived from whole cell fungal systems is still observed. 

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