title: Effect of guanine nucleotides on the conformation and stability of chloroplast elongation factor Tu.
abstract: The effect of guanine nucleotides and kirromycin on the conformation and stability of the chloroplast elongation factor Tu (EF-Tuchl) from Euglena gracilis has been investigated. Free EF-Tuchl is quite thermolabile but the protein is greatly stabilized by guanine nucleotides. The temperature dependence of the thermal inactivation of EF-Tuchl was used to calculate the amount of stabilization energy conferred by the guanine nucleotides. GDP increases the activation energy for the denaturation process by 77 kcal/mol while GTP increases the activation energy by 51 kcal/mol. The difference in heat stability of free EF-Tuchl and the EF-Tuchl.GDP complex was used to determine a dissociation constant of 1.3 x 10(-7) M at 37 degrees C. The temperature dependence of the dissociation constant allowed the calculation of a delta H degree obsd of -55 kcal/mol and a delta S degree obsd of -146 cal/(mol degree) for GDP binding to EF-Tuchl.EF-Tuchl was found to have a trypsin-sensitive region similar to that observed for Escherichia coli EF-Tu. This loop region was protected by GTP and kirromycin but not by GDP.
authors.affiliation: Department of Chemistry, University of North Carolina, Chapel Hill 27599-3290.
authors.forename: M A
authors.initials: MA
authors.lastname: Lapadat
authors.forename: L L
authors.initials: LL
authors.lastname: Spremulli
mesh_terms: D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D002736:Chloroplasts / Q000378:metabolism*; D004355:Drug Stability; D005056:Euglena gracilis / Q000378:metabolism*; D006153:Guanosine Diphosphate / Q000494:pharmacology; D006160:Guanosine Triphosphate / Q000494:pharmacology*; D007700:Kinetics; D010444:Peptide Elongation Factor Tu / Q000378:metabolism*; D011487:Protein Conformation; D011489:Protein Denaturation; D011728:Pyridones / Q000494:pharmacology; D013816:Thermodynamics
chemical_list: D000900:Anti-Bacterial Agents; D011728:Pyridones; D006153:Guanosine Diphosphate; D006160:Guanosine Triphosphate; D010444:Peptide Elongation Factor Tu; C008536:mocimycin