Erythrocyte isozymes of phosphofructokinase in genetically high- and low-2,3-diphosphoglycerate rats

A major locus (Dpg) with two alleles (d and D) controls erythrocyte 2,3-diphosphoglycerate (DPG) levels in Long-Evans rats and is closely linked to a locus (Hbb) determining a hemoglobin electrophoretic polymorphism. Glycolytic intermediate levels and phosphofructokinase (PFK) kinetic studies suggest that in vivo PFK activity differences underlie the differences in DPG levels. We report here chromatographic and immunologic evidence that rat erythrocyte PFK is composed of two isozymes which elute from DEAE-Sephadex at positions identical to those of the isozymes in platelets and liver, respectively. The percentage of platelet-type PFK is significantly (P less than 0.05) smaller in low-DPG (dd) hemolysates than in DD hemolysates regardless of hemoglobin phenotype. When hemolysates were prepared in a stabilizing buffer, PFK specific activity was significantly (P less than 0.005) higher in DD rats. These data suggest that the PFK kinetic differences may result from alterations in the isozyme composition of active PFK.     

Blocking of acidosis-mediated apoptosis by a reduction of lactate dehydrogenase activity through antisense mRNA expression.

Lactic acid produced from the cells is a potential cause of extra- and intracellular acidification. Due to scarce technical tools, lactic acid that leads to acidification could not be reduced and direct evidence of the relationship between metabolic lactate and apoptosis has not yet been elucidated. In this study, we designed a cellular pH regulation system in CHO cells by a reduction of lactate dehydrogenase (LDH) activity through LDH antisense mRNA expression. This inhibited lactate production and, therefore, acidification of the cytosol. Under HCO3(-)-buffered growth conditions, both the parent CHO cells and the engineered CHO cells maintained their extracellular pH and intracellular pH fairly well. However, upon acidification of the cytosol, only the parent CHO cells underwent apoptosis under HCO3(-)-free conditions. In fact, we observed a number of apoptosis-related events only in control cells, including mitochondrial dysfunction, cytochrome c release, and an increase in caspase-3 enzymatic activity.     

DNA cleavage and religation by human topoisomerase II alpha at high temperature.

A common DNA religation assay for topoisomerase II takes advantage of the fact that the enzyme can rejoin cleaved nucleic acids but cannot mediate DNA scission at suboptimal temperatures (either high or low). Although temperature-induced DNA religation assays have provided valuable mechanistic information for several type II enzymes, high-temperature shifts have not been examined for human topoisomerase IIalpha. Therefore, the effects of temperature on the DNA cleavage/religation activity of the enzyme were characterized. Human topoisomerase IIalpha undergoes two distinct transitions at high temperatures. The first transition occurs between 45 and 55 degrees C and is accompanied by a 6-fold increase in the level of DNA cleavage at 60 degrees C. It also leads to a loss of DNA strand passage activity, due primarily to an inability of ATP to convert the enzyme to a protein clamp. The enzyme alterations that accompany the first transition appear to be stable and do not revert at lower temperature. The second transition in human topoisomerase IIalpha occurs between 65 and 70 degrees C and correlates with a precipitous drop in the level of DNA scission. At 75 degrees C, cleavage falls well below amounts seen at 37 degrees C. This loss of DNA scission appears to result from a decrease in the forward rate of DNA cleavage rather than an increase in the religation rate. Finally, similar high-temperature alterations were observed for yeast topoisomerase II and human topoisomerase IIbeta, suggesting that parallel heat-induced transitions may be widespread among type II topoisomerases.     

A new statistical method for identifying interconnections between neuronal network elements

A new method is proposed to analyse dependencies in point processes, which takes into account specific character of neuronal activity. Simulation modelling of neuronal network revealed that the estimated weight of connection depends monotonically on the value of the model synaptic strength. In contrast to the crosscorrelation, the method allows for nonlinear interconnections and does not require point processes to be stationary and samples to be large. Examples are presented of the method's application to neurophysiological data analysis.