Research in the Miller Lab  




Phytase is an enzyme that catabolically produces myo-inositol and inorganic phosphate from phytic acid. Phytic acid is very plentiful in soybean meals and other legumes, and it binds essential minerals and hinders mineral nutrition in monogastric organisms including poultry, swine, and humans. Some grains have a natural level of phytase on the hull of the kernel while other grains have little or none. Wheat and rye are very high in naturally occurring phytase while corn and soybean meal are low, so when corn-based feed contains a phytase additive, the digestion of phytic acid in the animal is significantly improved. Undigested phytic acid found in animal species can also harm the environment, because it could be digested by microbially produced phytase and eventually contaminate groundwater. Phytase is becoming popular when producing animal feed, because with the addition of phytase, the animal has the ability to digest and utilize  more of the phosphorus produced from breaking down the phytic acid leading to decrease of phosphorus lost in their manure. With the growing popularity of phytase research, “phytase” is now considered a broad general classification that includes numerous structurally different enzymes. The focus of this research is to examine the optimal catalytic conditions of phytase as well as phytase activity in various animal feeds and the phosphorous levels in various animal environments.



Regulation of 11β-Hydroxysteroid Dehydrogenase

11b-hydroxysteroid dehydrogenase type 1 (11b-HSD-1) catalyzes the conversion of inactive 11-keto-metabolites (cortisone and 11-deoxycorticosterone) into active glucocorticoids (cortisol and corticosterone).  Glucocorticoids are lipophilic steroids that regulate many physiological processes such as carbohydrate and lipid metabolism, development, blood pressure, and immunity.  Glucocorticoids exert their effect by binding to a specific nuclear receptor and activating or repressing gene transcription.  An increase in the activation of glucocorticoid receptors has been shown to result in metabolic disorders such as central obesity, insulin resistance, and Type II diabetes.  Since 11b-HSD-1 is responsible for the metabolism of glucocorticoids, inhibition of 11b-HSD-1 has been proposed as a novel therapeutic in insulin resistant syndromes such as diabetes and obesity.   However, 11b-HSD-1 is a bidirectional enzyme depending on the redox state of NADP(H) in a particular cell.  In the liver, 11b-HSD-1 primarily has reductase activity thereby converting inactive glucocorticoids into active glucocorticoids.  In various reproductive tissues, 11b-HSD-1 primarily has oxidative activity thereby converting active glucocorticoids into inactive glucocorticoids.  In addition to the bidirectionality of the enzyme, 11b-HSD-1 is highly regulated.  Although the mechanism is not understood, in obese humans, the conversion of cortisone (inactive glucocorticoid) to cortisol (active glucocorticoid) by 11b-HSD-1 is impaired in the liver but is increased in adipose tissue.  Therefore, understanding the tissue-specific functions of 11b-HSD-1 is important to gain insight into the approaches of target experimental and therapeutic manipulations.  The focus of this research is to determine the tissue specific metabolism and substrate specificity of 11b-HSD-1.


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