Structural studies on the plant plasma membrane calcium-ATPase

The plasma membrane Ca$\sp{2+}$-ATPase is a ubiquitous membrane protein that mediates the active transport of calcium out of the cytoplasm into the cell exterior. In plant cells it is believed to play a major regulatory role in signal transduction by helping to maintain a large gradient of calcium across the plasma membrane, thereby keeping the cell poised for response to environmental and hormonal cues. Research using isolated membrane vesicles has resulted in the study of the plasma membrane Ca$\sp{2+}$-ATPase, most of which has focused on characterization of its calcium transport properties. In this study a biochemical approach was taken to examine the essential amino acid residues which may be involved in the mechanism of the enzyme. For this, chemical modification reagents were used. In addition radiation inactivation analysis was used to examine the quaternary structure of the enzyme. The study of the plant plasma membrane Ca$\sp{2+}$-ATPase was conducted using vesicles isolated from red beet (Beta vulgaris L.) storage tissue which provided a means to examine the protein in its native state in the membrane. This work was conducted in order to have a better understanding of the function of the plasma membrane Ca$\sp{2+}$-ATPase and thereby establish structure-function relationships. In this investigation, chemical modification reagents such as phenylglyoxal and 2,3-butanedione were used to determine whether arginine residues are involved in the mechanism of the plasma membrane Ca$\sp{2+}$-ATPase. In addition, the reagents diethylpyrocarbonate, n-ethylmaleimide and erythrosin isothiocyanate were used to determine whether histidine, cysteine and lysine residues are involved in the mechanism of the enzyme respectively. All reagents inhibited both transport and hydrolytic properties of the enzyme. Therefore the results indicate that the above residues are involved in the activity of the enzyme, of which arginine residues derivitized by the reagents indicated, are probably located at or near the active site. Radiation inactivation analysis studies on the red beet plasma membrane Ca$\sp{2+}$-ATPase resulted in the determination of the target molecular size of the enzyme to be 245 kDa, and that the enzyme may function as a dimer in its native state. Results from this study provide information for further research on the structure of the plant plasma membrane Ca$\sp{2+}$-ATPase and the establishment of its role in signal transduction in plants.U of I OnlyETDs are only available to UIUC Users without author permissio