Accessory enzymes

Accessory DHPS enzymes confer resistance to sulfonamides. Two different types encoded by the genes sull (located on transposons) and sulll (located on plasmids) have been described. These resistance determinants are often genetically linked to trimethoprim resistance genes. Therefore, the combination of sulfonamide antibiotics with trimethoprim does not prevent resistance selection. 

Chlorophyll b occurs as an accessory pigment of the light-harvesting systems in land plants and green algae, and comprises one-third (or less) of total chlorophyll. The biosynthesis of chlorophyll b has been an area of active research particularly regarding its compartmentalization in chloroplast membranes, identification of the gene for chlorophyllide a oxidase, and characterization of the enzymes involved. ... 

The availability of these novel enzymes, next to the known pectic enzymes, offer new opportunities to use them as analytical tools in revealing the structure of oligo- and polysaccharides [31,32]. In contrast with frequently used chemical degradation methods, which usually have a poor selectivity, these enzymes act in a deflned way. To be able to recognize different structural units within the polymer, endo-acting types of enzyme are preferred, although accessory enzymes might be essential as well [30]. 

As an accessory enzyme for the RGases, rhamnogalacturonan acetyl esterase (RGAE) was discovered in the same A. aculeatus preparation. This enzyme appeared to be specific for the de-acetylation of MHR and essential for the degradation of MHR by RGases A and B. 

Nakajima T., Sakaue M.K., Saito S., Ogawa K. and Taniguchi K. (1998). Immuno-histochemical and enzyme-histochemical study on the accessory olfactory bulb of the dog. Anat Rec 252, 393-402. 

The specific behaviour of unsaturated fatty acids under oxidation is determined by the position and the number of double bonds in the fatty acid molecule. The stepwise oxidation of an unsaturated acid to the position of a double bond in it proceeds in a manner similar to that of saturated acid oxidation. If the double bond retains the same configuration (trans-configuration) and position (A2,3) as those of the enoyl-CoA, which is produced during the oxidation of saturated fatty acids, the subsequent oxidation proceeds via conventional route. Otherwise, the oxidation reaction proceeds with the involvement of an accessory enzyme, A3,4-CiS-A2,3jrans-enoyl-CoA isomerase this facilitates the translocation of the double bond to an appropriate position and alters the double-bond configuration from cis to trans. 

N. Drapal, A. Bock (1998) Interaction of the hydrogenase accessory protein HypC with HycE, the large subunit of Escherichia coli hydrogenase 3 during enzyme maturation. Biochemistry, 37 2941-2948... 

Figure 9.1 CYP catalytic cycle. The sequential two-electron reduction of CYP and the various transient intermediates were first described in the late 1960s [206], The sequence of events that make up the CYP catalytic cycle is shown. The simplified CYP cycle begins with heme iron in the ferric state. In step (i), the substrate (R—H) binds to the enzyme, somewhere nearthe distal region of the heme group and disrupts the water lattice within the enzymes active site [207], The loss of water elicits a change in the heme iron spin state (from low spin to high spin) [208]. Step (ii) involves the transfers of an electron from NADPH via the accessory flavoprotein NADPH-CYP reductase, with the electron flow going from the reductase prosthetic group FAD to FMN to the CYP enzyme [206,209]. The...

The development of biological tools to support DDI studies has paralleled the development of bioanalytical techniques. To better understand in vitro-in vivo (IVIV) correlations, the effects of differences in enzyme preparations and incubation conditions must be understood. Differences between enzyme preparations include nonspecific binding, the ratio of accessory proteins (cytochrome b5 and reductase) to CYPs and genetic variability differences in incubation conditions include buffer strength, the presence of inorganic cations and solvent effects. Understanding how biology influences enzymatic activity is crucial to accurate and consistent prediction of the inhibition potential. 

Eukaryotic genomes contain information for more than 20 E2s and hundreds of E3s. In contrast to the wealth of components devoted to marking protein substrates for destruction, only one enzyme, the 26S proteasome, has been found to degrade ubiquitylated proteins. However, there is complexity here as well, since the 26S proteasome is an assemblage of at least 30 different subunits. Moreover, there is a growing list of proteins that act as proteasome activators, adapters, or accessory factors. In this chapter I focus on basic biochemical and physiological properties... 

The N-terminal extensions are removed thereby generating a new unblocked N-terminal threonine in the catalytically active yS-subunits. A small accessory protein called Umpl in yeast or proteassemblin in mammalian cells assists in the final assembly of the 20S proteasome [132], Interestingly Umpl/POMP is apparently trapped in the proteasome s central chamber and degraded upon maturation of the enzyme [133]. 

Figure 6.3. Alignments of regions identified to be important in nickel accessory proteins for maturation of the final nickel sink, the nickel-containing enzyme. A, The His-rich regions of known or putative HypB proteins and the UreE and CooJ proteins from various organisms. Reprinted with permission from Olson and Maier (2000). B, Alignment of the G motifs from known or putative HypB proteins and the related nucleotide-binding P-loop residues (in the G1 region) of CooC and UreG. (Adapted from Olson and Maier (2000).

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