Biomaterial Database

The isozymes of glucose-phosphate isomerase (GPI-A2 and GPI-B2) from the teleost fish Fundulus heteroclitus (L.). 1985

R J Van Beneden, and D A Powers

The fish, Fundulus heteroclitus (L.), like most advanced teleosts, possesses duplicate loci for the glycolytic enzyme, glucose-phosphate isomerase (D-glucose-6-phosphate ketol-isomerase, EC 5.3.1.9). The locus for the GPI-A2 (where GPI represents glucose-phosphate isomerase) isozyme is preferentially expressed in anaerobic tissues such as white skeletal muscle, while GPI-B2 predominates in aerobic tissues like liver and red muscle. We questioned whether this tissue specificity would be reflected in unique structural and functional characteristics of the respective isozymes. Consequently, an analysis of the two isozymes was undertaken. The enzymes were purified by a combination of ion-exchange chromatography and isoelectric focusing. Each isozyme was characterized as to native and subunit molecular weight, isoelectric pH, and susceptibility to thermal denaturation. Both were dimeric enzymes, with native molecular masses of 110 kDa. The isoelectric pH values for GPI-A2 and GPI-B2 were 7.9 and 6.4, respectively. Differences were apparent in thermal stability, i.e. GPI-A2 was more stable than GPI-B2. Kinetic properties were investigated as a function of both pH and temperature. The Km values for fructose 6-phosphate (Fru-6-P) differed between the isozymes at low pH, but no significant differences were observed at higher pH. The inhibition constant (Ki) for 6-phosphogluconate (6-P-gluconate) was pH dependent. GPI-A2 was slightly more sensitive to 6-P-gluconate inhibition than GPI-B2 between pH 7.0 and 8.5. The Km for Fru-6-P was temperature dependent for the GPI-B2 isozyme, but relatively temperature independent for GPI-A2 between 10 and 35 degrees C. The Ki for 6-P-gluconate was temperature dependent for both isozymes. The Ki values for GPI-A2 were consistently lower than those for GPI-B2. Energies of activation differed between the two isozymes by 4.4 kcal with GPI-A2 having the lower value. While delta G values were identical for the isozymes, their delta H and delta S values differed significantly. The structural and kinetic differences that exist between the glucose-phosphate isomerase isozymes appear to be tailored to the unique metabolic demands of the tissues in which these Gpi loci are expressed.

UI	MeSH Term	Description	Entries
D007527	Isoenzymes	Structurally related forms of an enzyme. Each isoenzyme has the same mechanism and classification, but differs in its chemical, physical, or immunological characteristics.	Alloenzyme,Allozyme,Isoenzyme,Isozyme,Isozymes,Alloenzymes,Allozymes
D007700	Kinetics	The rate dynamics in chemical or physical systems.
D008099	Liver	A large lobed glandular organ in the abdomen of vertebrates that is responsible for detoxification, metabolism, synthesis and storage of various substances.	Livers
D008970	Molecular Weight	The sum of the weight of all the atoms in a molecule.	Molecular Weights,Weight, Molecular,Weights, Molecular
D011489	Protein Denaturation	Disruption of the non-covalent bonds and/or disulfide bonds responsible for maintaining the three-dimensional shape and activity of the native protein.	Denaturation, Protein,Denaturations, Protein,Protein Denaturations
D005399	Fishes	A group of cold-blooded, aquatic vertebrates having gills, fins, a cartilaginous or bony endoskeleton, and elongated bodies covered with scales.
D005956	Glucose-6-Phosphate Isomerase	An aldose-ketose isomerase that catalyzes the reversible interconversion of glucose 6-phosphate and fructose 6-phosphate. In prokaryotic and eukaryotic organisms it plays an essential role in glycolytic and gluconeogenic pathways. In mammalian systems the enzyme is found in the cytoplasm and as a secreted protein. This secreted form of glucose-6-phosphate isomerase has been referred to as autocrine motility factor or neuroleukin, and acts as a cytokine which binds to the AUTOCRINE MOTILITY FACTOR RECEPTOR. Deficiency of the enzyme in humans is an autosomal recessive trait, which results in CONGENITAL NONSPHEROCYTIC HEMOLYTIC ANEMIA.	Glucosephosphate Isomerase,Phosphoglucose Isomerase,Phosphohexose Isomerase,Autocrine Motility Factor,Isomerase, Glucose 6 Phosphate,Neuroleukin,Tumor Autocrine Motility Factor,Tumor-Cell Autocrine Motility Factor,Factor, Autocrine Motility,Glucose 6 Phosphate Isomerase,Isomerase, Glucose-6-Phosphate,Isomerase, Glucosephosphate,Isomerase, Phosphoglucose,Isomerase, Phosphohexose,Motility Factor, Autocrine,Tumor Cell Autocrine Motility Factor
D006863	Hydrogen-Ion Concentration	The normality of a solution with respect to HYDROGEN ions; H+. It is related to acidity measurements in most cases by pH	pH,Concentration, Hydrogen-Ion,Concentrations, Hydrogen-Ion,Hydrogen Ion Concentration,Hydrogen-Ion Concentrations
D000818	Animals	Unicellular or multicellular, heterotrophic organisms, that have sensation and the power of voluntary movement. Under the older five kingdom paradigm, Animalia was one of the kingdoms. Under the modern three domain model, Animalia represents one of the many groups in the domain EUKARYOTA.	Animal,Metazoa,Animalia
D013816	Thermodynamics	A rigorously mathematical analysis of energy relationships (heat, work, temperature, and equilibrium). It describes systems whose states are determined by thermal parameters, such as temperature, in addition to mechanical and electromagnetic parameters. (From Hawley's Condensed Chemical Dictionary, 12th ed)	Thermodynamic