Enzymes comparisons

Robinson, M.K., et al., Use of the mouse intranasal test (MINT) to determine the allergenic potency of detergent enzymes comparison to the guinea pig intratracheal (GPIT) test, Toxicol. Set, 43, 39, 1998. 

Yamazaki, H., Suzuki, M., Tane, K., Shimada, N., Nakajima, M. and Yokoi, T. (2000) in vitro inhibitory effects of troglitazone and its metabolites on drug oxidation activities of human cytochrome P450 enzymes comparison with pioglitazone and rosiglitazone. Xenobiotica, 30 (1), 61—70. 

An important issue in analyzing HIV-1 RT is the flexibility of the enzyme. Comparison of structures of unliganded HIV-1 RT and NNRTI-bound HIV-1 RT complexes has shown that the NNIBP is not present in the unliganded form [34,41,43]. This underscores the importance of searching both the unliganded HIV-1 RT and the HIV-1 RT complexes with inhibitors and substrates in order to identify any potential inhibitor-binding sites. 

The first approach provides a simple interpretation of the capacity of a particular P450 form to metabolize a xenobiotic relative to other P450 enzymes. Comparison is straightforward, requiring knowledge of the expression level in the cDNA expression system and verification of linearity of the system. It may also be appropriate to adjust data for differences in OR levels if these levels vary for the different cDNA-expressed enzymes. Unless the enzyme specificity is absolute or nearly absolute, this approach cannot establish the principal involved in metabolism because all enzymes are not equally abundant in vivo. 

Type II restriction enzymes are prevalent in Archaea and Eubacteria. What can we tell of the evolutionary history of these enzymes Comparison of the amino acid sequences of a variety of type II restriction endonucleases did not reveal significant sequence similarity between most pairs of enzymes. However, a carefiil examination of three-dimensional structures, taking into account the location of the active sites, revealed the presence of a core structure conserved in the different enzymes. This structure includes P strands that contain the aspartate (or, in some cases, glutamate) residues forming the magnesium ion binding sites (Figure 9.44). 

Aspartate aminotransferase is the prototype of a large family of PLP-dependent enzymes. Comparisons of amino acid sequences as well as several three-dimensional structures reveal that almost all transaminases having roles in amino acid biosynthesis are related to aspartate aminotransferase by divergent evolution. An examination of the aligned amino acid sequences reveals that two residues are completely conserved. These residues are the lysine residue that forms the Schiff base with the pyridoxal phosphate cofactor (lysine 258 in aspartate aminotransferase) and an arginine residue that interacts with the a-carboxylate group of the ketoacid (see Figure 23.11). 

Tuovinen, O.H., Kelly, B.C. and Nicholas, D.J.D., 1976. Enzymic comparison of the inorganic sulfur metabolism in autotrophic and heterotrophic Thiobacillus ferrooxidans. Can. J. Microbiol., 22 109—113. 

Figure 1 In a QM/MM calculation, a small region is treated by a quantum mechanical (QM) electronic structure method, and the surroundings treated by simpler, empirical, molecular mechanics. In treating an enzyme-catalysed reaction, the QM region includes the reactive groups, with the bulk of the protein and solvent environment included by molecular mechanics. Here, the approximate transition state for the Claisen rearrangement of chorismate to prephenate (catalysed by the enzyme chorismate mutase) is shown. This was calculated at the RHF(6-31G(d)-CHARMM QM-MM level. The QM region here (the substrate only) is shown by thick tubes, with some important active site residues (treated by MM) also shown. The whole model was based on a 25 A sphere around the active site, and contained 4211 protein atoms, 24 atoms of the substrate and 947 water molecules (including 144 water molecules observed by X-ray crystallography), a total of 7076 atoms. The results showed specific transition state stabilization by the enzyme. Comparison with the same reaction in solution showed that transition state stabilization is important in catalysis by chorismate mutase78.

Because of the heterogeneous nature of methloninase catalysis (Figure 1), measurement of alpha-ketobutyrlc acid (as well as other carbonyls that may be present) may not provide accurate Indications of the activity of the enzyme. Comparison of the data in Figure 2 for cell-free extracts and semi-purified freeze dried methloninase solutions suggests that either protease activity was involved or that complex Interactions of potential substrates and products occurred. Use of alpha-ketobutyrlc acid assays for methloninase activity in samples Incubated for prolonged periods seems potentially vulnerable to such analytical pitfalls. 

Salhab AS, James MO. Wang SL, et al. 1987. Formation of benzo( a)pyrene-DNA adducts by microsomal enzymes Comparison of maternal and fetal liver, fetal hematopoietic cells and placenta. 

SARLO, K., POLK, J.E., RITZ, H.L. (1991) Guinea pig intratracheal test toassess respiratory allergenicity of detergent enzymes comparison with the human data base. Journal of Allergy and Clinical Immunology, 87, 816. 

Additional information <1> (<1> biphasic pH profile with two optima at pH 6.8 and 10.0 and a minimum at 8.5, comparison of pH optima of N- and C-deletion mutants of enzyme, comparison of kinetic properties of wild-type and deletion mutants at pH 6.8 and pH 8.2 [45] <1> comparison of pH-pro-files of wild-type and mutant enzymes [49]) [45, 49]... 

Active immobilized enzyme comparison of the properties of the soluble and insoluble enzymes... 

Active immobilized enzyme comparison 540 of different preparation procedures... 

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