ORIGINAL_ARTICLE
REASSOCIATION AND REACTIVATION OF GLUCOSE 6-PHOSPHATE DEHYDROGENASE FROM STREPTOMYCES AUREOFACIENS AFTER DENATURATION BY 6 M UREA
Glucose 6-phosphate dehydrogenase (G6PD) from Streptomyces aureofaciens was purified and denatured in 6 M urea. Denaturation led to complete dissociation of the enzyme into its inactive monomers, 98% loss of the enzyme activity, about 30% decrease in the protein fluorescence and a 10 nm red shift in the emission maximum. Dilution of urea-denatured enzyme resulted in regaining of the enzyme activity and the native protein fluorescence. The renatured enzyme was indistinguishable from the native enzyme based on a number of enzymological and physicochemical criteria. Regaining of the protein fluorescence occurred immediately after diluting the denatured enzyme and before reactivation started. The reactivation process was also monitored by measuring the accessibility of histidine residues toward diethylpyrocarbonate modification. As the reactivation proceeded, less histidine residues were able to be modified. Nicotineamide adenine dinucleotide (NAD+), nicotinamide adenine dinucleotide phosphate (NADP+) and glucose 6-phosphate stimulated the reactivation rate at different degrees. It seemed likely that specific ligands stimulated reactivation by binding to an inactive form of the enzyme leading to a different pathway of refolding. The data are consistent with a model for enzyme renaturation and reactivation in which NAD+ and NADP+ pull the enzyme toward different conformational structures.
https://jsciences.ut.ac.ir/article_31679_f082f92fd9388163c301e5354dc908c6.pdf
2003-06-01
ORIGINAL_ARTICLE
INVESTIGATION OF REASONS THAT IMPLY THE DIMINISHED INCLUSION BODIES IN E. COLI
https://jsciences.ut.ac.ir/article_31680_1bdbe88abbba143985482dd21ec84f9f.pdf
2003-06-01
ORIGINAL_ARTICLE
MEIOTIC STUDIES OF SOME AVENA SPECIES AND POPULATIONS IN IRAN
Eleven populations of five Avena species were analysed for meiotic characters including chiasma frequency and distribution as well as chromosomal association and segregation. Plants of a single population of A. eriantha showed the presence of 2n = 14 (diploid) and 2n = 4x = 28 chromosome number. Populations of A. barbata and A. wiestii possessed n = 14, while populations of A. sterilis ssp. ludoviciana possessed 2n = 6x = 42 (hexaploid) chromosome number. Tetraploid and hexaploid species showed diplontic behavior and formed only bivalents. The species and populations studied differed significantly in the frequency of chiasmata. B-chromosomes occurred in some of the species studied. Cytomixis and chromosome elimination led to aneuploid and unreduced pollen mother cell formation in the species studied.
https://jsciences.ut.ac.ir/article_31681_2225bb8060f5d5c78a26e68475fa4f0d.pdf
2003-06-01
ORIGINAL_ARTICLE
EXCESS THERMODYNAMIC PROPERTIES CALCULATIONS FOR ALCOHOLS IN INERT SOLVENTS BASED ON FOURIER TRANSFORM INFRARED SPECTROSCOPY MEASUREMENTS
Self-association of alcohols; including ethanol, methanol, cyclopentanol and octanol in separate mixtures with inert solvents have been studied using FT-IR spectroscopy. Except for the band at 3640 cm–1 in the IR spectrum of the alcohols which is due to the monomer species, the presence of other bands in the region of stretching vibrational frequencies of OH (3100-3700 cm–1) are attributed to the higher associated species such as dimmer, trimer and multimers. Association models of such as trimer, continuous linear association model, linear association with cyclic trimer (LACT) and dependent equilibrium constant model (DECM) have been used for treating the IR Spectroscopy results. The calculations indicated that the dominant species in the studied concentration range of alcohols is the trimer. The evaluated association constants in the best-fitted model (timer or LACT) were utilized to obtain the excess properties such as hE, gE and activity coefficients for the mixtures.
https://jsciences.ut.ac.ir/article_31682_13a1f891e8e7bd06b41afbeec5f3f087.pdf
2003-06-01
ORIGINAL_ARTICLE
AGAINST THE VALIDITY OF THE CLOSED SYSTEM MODEL FOR CALCULATING
OSMOTIC PRESSURE
This paper criticizes the model and the new definition for osmotic pressure given by Parsafar et al. [J. Sci. I. R. Iran, Vol. 10, No. 4, 233 (1999)]. The model is a closed system containing 1 kg of solvent plus m mole of solute at constant temperature and under pressure P0 + ? where P0 is the standard pressure and ? is the osmotic pressure of the corresponding m molal solution. While the total number of moles, temperature and pressure of the system are specified, the volume of the system has also been specified. The volume of the solution under pressure P0 + ? is claimed to be the same as the volume of 1 kg of pure solvent under the standard pressure P0. The present work shows that the two volumes can not be the same and their difference is not negligible. The use of an equation of state to calculate osmotic pressure and activity by Parsafar et al. has also been questioned.
https://jsciences.ut.ac.ir/article_31683_701e7b15b5f9a22ffbffbbec060ca11e.pdf
2003-06-01
ORIGINAL_ARTICLE
WARM TO COLD WATER CARBONATE FORMATION DURING THE ORDOVICIAN AND THE JURASSIC: EXAMPLES FROM IRAN, AUSTRALIA, AND ENGLAND
Isotope data from bulk carbonates, micrite, marine calcite cements, non-skeletal grains and brachiopods indicate deposition of a wide spectrum of warm to cold water carbonates during the Ordovician and the Jurassic. This isotopic interpretation is supported by warm to cold climatic models proposed for the Ordovician and the Jurassic. These carbonates formed during the Greenhouse mode (conditions similar to present day) and Icehouse mode. Isotopic equilibrium trends of carbonate minerals indicate an originally aragonite-calcite mixture during the late Ordovician of Tasmania and Late Jurassic of Iran (Kopet-Dagh Basin-Sarakhs area) corresponding to warm temperatures; whereas originally calcitic mineralogy deposited during the Mid Jurassic in England and Scotland, and the Late Jurassic at Mallorca Island, Spain, correspond to cool to cold water temperatures. Sedimentological features of these ancient limestones are similar to modern warm to cold water carbonates.
https://jsciences.ut.ac.ir/article_31684_c32e35e6fe46e79555c99191e067af4d.pdf
2003-06-01
ORIGINAL_ARTICLE
SOGHAN COMPLEX AS AN EVIDENCE FOR PALEOSPREADING CENTER AND MANTLE DIAPIRISM IN SANANDAJ-SIRJAN
ZONE (SOUTH-EAST IRAN)
https://jsciences.ut.ac.ir/article_31685_02d519463548da0b9dc93843527737aa.pdf
2003-06-01
ORIGINAL_ARTICLE
COVARIANCE MATRIX OF MULTIVARIATE REWARD PROCESSES WITH NONLINEAR REWARD FUNCTIONS
Multivariate reward processes with reward functions of constant rates, defined on a semi-Markov process, first were studied by Masuda and Sumita, 1991. Reward processes with nonlinear reward functions were introduced in Soltani, 1996. In this work we study a multivariate process , , where are reward processes with nonlinear reward functions respectively. The Laplace transform of the covariance matrix, ?(t), is specified for given , and if they are real analytic functions, then the covariance matrix is fully specified. This result in particular provides an explicit formula for the variances of univariate reward processes. We also view ?(t) as a solution of a renewal equation.
https://jsciences.ut.ac.ir/article_31686_fb794790eb54782a750228e2b44912a8.pdf
2003-06-01