This book is aimed to provide a full characterization of the thermal behavior of xylose isomerase extracted from Cereus pterogonous, not only in terms of kinetics but also for the first time to our knowledge via the determination of the thermodynamic parameters of heat inactivation. It is believed that this work will continue into a cascade of discoveries related to the existence and function of the thermostable enzymes in the eukaryotic domain that will find use in commerce, industry and perhaps even in clinical medicine. It is expected that the present book will serves as an important step to understanding and appreciate the role of thermal behavior of an enzyme by heat inactivation.