Ancillary Enzymes

Ancillary enzymes Glutathione reductase (uses NADPH) NADPH-delivering enzymes... 

Microorganisms contain a multitude of enzyme systems, some of which arc not directly involved in their use in chemical oxidations, but which are necessary for the cell to function in total. As discussed previously these ancillary enzymes can be harmful, and ways of reducing or avoiding their effects have been sought two of these are considered in the following sections. 

Several ancillary enzymes support glutathione peroxidase function (Figure 10.21). GSH is regenerated from GSSG by glutathione reductase ... 

Metabolic disorders of urea biosynthesis, while extremely rare, illustrate four important principles (1) Defects in any of several enzymes of a metabolic pathway enzyme can result in similar clinical signs and symptoms. (2) The identification of intermediates and of ancillary products that accumulate prior to a metabolic block provides insight into the reaction that is impaired. (3) Precise diagnosis requires quantitative assay of the activity of the enzyme thought to be defective. (4) Rational therapy must be based on an understanding of the underlying biochemical reactions in normal and impaired individuals. 

Purified membrane proteins or enzymes can be incorporated into these vesicles in order to assess what factors (eg, specific lipids or ancillary proteins) the proteins require to reconstitute their function. Investigations of purified proteins, eg, the Ca " ATPase of the sarcoplasmic reticulum, have in certain cases suggested that only a single protein and a single lipid are required to reconstitute an ion pump. 

Pathway alternations are made with the express purpose of improving a given metabolic process. We generally view these modifications of catabolic pathways as the addition or modification of existing catabolic enzymes. However, certain ancillary pathways and enzymes exist that are not necessary to the catabolism of a given substrate, yet nevertheless can influence the overall metabolic process. 

Of the complexes studied, those with ancillary ligands that contain sulfur atoms have received the most attention. Among the most studied are the bis(dial-kyldithiocarbamate) molybdenum oxido complexes [196,197], Unfortunately, although these complexes react with certain enzyme substrates, their common problem as models for Moco active sites involves the propensity of the Movl dioxo and MoIV monoxo complexes to form a comproportionated Mov p-oxido dimer (Eq. 13 dtc = diethyldithiocarbamate). 

Intramolecular heterolytic cleavage of H2 is one of the oldest reactions of H2 and is among the first homogeneous catalytic conversions. r 2-H2 can protonate a counteranion or a basic ancillary ligand, either at the M-L bond or at a ligand lone pair. Intramolecular heterolysis of H H is most likely an essential step in many diverse systems ranging from industrial processes to the function of metallo enzymes such as... 

RNA polymerases require ancillary factors (proteins) for active transcription these are called transcription factors. The enzyme together with these factors constitutes the basal transcription apparatus. 

Ferrans et al. (1969) noted ultrastructural changes in myofibrils, including mitochondrial swelling and disorganization. Catecholamines also produce changes in the activity of oxidative enzymes. The decline in the activity progresses to the point where necrosis is evident. Ancillary effects include loss of myocardial potassium and an increase in interstitial fluid. Intracellular calcium overload also develops as noted by Fleckenstein et al. (1974). It has been hypothesized that necrosis due to catecholamine overload may be caused by a defect in energy supply needed for the maintenance of cellular processes. 

In direct enzyme assays, the initial rate can be determined readily and this is the quantity that should be used to specify enzyme activity. However, the situation is more complex in coupled reactions, since there is usually a lag phase as the intermediate product is made. For determination of enzyme activity, it is essential that the rate of the ancillary reaction is not a limiting factor, which means that the activity of the coupled enzyme should be in sufficient excess (> 10-fold) over that of the enzyme of interest. 

Fatty acids that contain double bonds or odd numbers of carbon atoms require ancillary steps to be degraded. An isomerase and a reductase are required for the oxidation of unsaturated fatty acids, whereas propionyl CoA derived from chains with odd numbers of carbons requires a vitamin Bj2-dependent enzyme to be converted into succinyl CoA. 

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