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N-acetyl transferase (NAT) is responsible to catalyze the transfer of acetyl groups to arylamines from acetyl-CoA. Aralkylamine Nacetyl transferase (AANAT), which belongs to GCN5-related N-acetyl transferase member, is a globular 23-kDa cytosolic protein that forms a reversible regulatory complex with 14-3-3 proteins, AANAT regulates the daily cycle of melatonin biosynthesis in mammals, making it an attractive target for therapeutic control of abnormal melatonin production in mood and sleep disorders. There is no evidence available regarding α and β subunits, active site and their ASA value in Dopamine N-acetyl transferase. Therefore, we describe the development of Dopamine N-acetyl transferase model in Tribolium castaneum. We further document the predicted active sites in the structural model with solvent exposed ASA residues. During this study, the model was built by CPH program and validated through PROCHECK, Verify 3D, ERRAT and ProSA for reliability. The active sites were predicted in the model with further ASA analysis of active site residues. The discussed information thus provides insight to the predicted active site and ASA values of Dopamine N-acetyl transferase model in Tribolium castaneum.

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Threonine degradation involves three key enzymes that lead to three different pathways. These are threonine dehydrogenase, threonine dehydratase and threonine aldolase. A search for homologues of these enzymes has revealed the presence of threonine dehydratase and threonine aldolase in the genomes of hyperthermophilic bacteria. Among the hyperthermophilic archaea, threonine dehydrogenase is present in members of Euryarchaeota, whereas threonine dehydratase is found in members of Crenarchaeota. In fact, threonine dehydrogenase has been characterized from several members of the Euryarchaeota. Based on the enzymes studied as well as on the presence of gene homologues, it can be postulated that all three pathways exist in hyperthermophiles. In this chapter, these three metabolic pathways, their presence or absence in a particular hyperthermophile and an account of the thermostable enzymes involved in the pathways are described.

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The enzyme dihydrofolate reductase (DHFR) catalyzes NADPH dependent reduction of dihydrofolate to tetrahydrofolate. It plays a crucial role in the DNA synthesis. The investigation of evolution of DHFR generates immense curiosity. It aids in predicting how the enzyme has adapted to the surroundings of various cell types. In spite of great similarity in the structure of E. coli DHFR and human DHFR, their primary sequences are divergent to a great extent, which is evident in variations in the kinetics mechanism of their catalysis. In presence of physiological levels of ligands, they possess distinct kinetics and different rate limiting steps. We have reviewed the process of their unfolding and refolding, their behaviour in denaturing conditions and in presence of various chaperones. Although there is structural similarity between these two homologous enzymes yet they have established distinct mechanisms to accomplish the coequal functions.