Nitrogenase activity of immobilized Azotobacter vinelandii.

As part of a program to investigate the use of biological nitrogen fixation for fertilizer ammonia production, an investigation into the immobilization of the aerobic, nitrogen-fixing bacterium, Azotobacter vinelandii was undertaken. Immobilization was acaccomplished by adsorption onto an anionic exchange cellulose (Cellex E) with loadings as high as 10' cells/g resin. Immobilized cell preparations were tested under both batch and continuous-flow conditions. Nitrogenase activities as high as 4200 nmol/min g resin were observed as measured by the acetylene reduction assay. Immobilized cells retained their activity for as long as 117 hr in a continuous-flow reactor. Activity loss appeared to be related to the development of a variant strain.     

Serum creatine kinase activity following repeated bouts of isometric exercise with different muscle groups

The purpose of this study was to examine the relationship between the muscle mass involved in exercise and post-exercise serum creatine kinase (CK) elevation. Twelve untrained college-aged men completed three isometric exercises: one arm flexion (OAF), two arm flexion (TAF) and one leg knee extension (OLE). These exercises were balanced over subjects and days and separated by two week intervals. Each exercise consisted of 40 maximal isometric concentrations lasting for 10 s with a 20 s rest between contractions. Relative increases in serum CK for OAF, TAF, and OLE were 181 +/- 70% (SD), 222 +/- 69% and 297 +/- 67%, respectively. An ANOVA using a latin square design for analysis of carry over effects showed that these CK increases were not significantly different (p greater than 0.05). However, the increase in serum CK following the first exercise (379 +/- 90%), regardless of what it was (OAF, TAF, or OLE), was significantly greater (p less than 0.05) than those following bouts 2 and 3 (155 +/- 29%; 167 +/- 54%). Regression analysis indicated that post-exercise serum CK elevation was not related to the amount of muscle mass involved in the exercise (r = 0.30, p greater than 0.05) nor to muscle tension developed (r = 0.28, p greater than 0.05). We conclude that post-exercise serum CK elevation is not necessarily related to the muscle mass involved in the exercise. Because each exercise involved the use of different muscle groups, factors outside the exercising muscle may contribute to post-exercise serum enzyme activity.     

The Effect of Marsh Age on Ecosystem Function in a Rapidly Transgressing Marsh

Ecosystems - Sea-level rise is leading to the migration of marshes into coastal forests throughout North America. Marsh migration represents a primary mechanism for marsh survival in the face of...     

Continuous-time modeling of cell fate determination in Arabidopsis flowers

Background  

The genetic control of floral organ specification is currently being investigated by various approaches, both experimentally and through modeling. Models and simulations have mostly involved boolean or related methods, and so far a quantitative, continuous-time approach has not been explored.     

A moderate glycemic meal before endurance exercise can enhance performance

Kirwan, John P., Donal O'Gorman, and William J. Evans.A moderate glycemic meal before endurance exercise can enhance performance. J. Appl. Physiol. 84(1):53-59, 1998.The purpose of this study was to determine whetherpresweetened breakfast cereals with various fiber contents and amoderate glycemic index optimize glucose availability and improveendurance exercise performance. Six recreationally active women ate 75 g of available carbohydrate in the form of breakfast cereals: sweetenedwhole-grain rolled oats (SRO, 7 g of dietary fiber) or sweetenedwhole-oat flour (SOF, 3 g of dietary fiber) and 300 ml of water orwater alone (Con). The meals were provided 45 min before semirecumbentcycle ergometer exercise to exhaustion at 60% of peakO₂ consumption (O_{2 peak}). Diet andphysical activity were controlled by having the subjects reside in theGeneral Clinical Research Center for 2 days before each trial. Bloodsamples were drawn from an antecubital vein for glucose, free fattyacid (FFA), glycerol, insulin, epinephrine, and norepinephrinedetermination. Breath samples were obtained at 15-min intervals aftermeal ingestion and at 30-min intervals during exercise. Muscle glycogenconcentration was determined from biopsies taken from the vastuslateralis muscle before the meal and immediately after exercise. PlasmaFFA concentrations were lower (P < 0.05) during the SRO and SOF trials for the first 60 and 90 min ofexercise, respectively, than during the Con trial. Respiratory exchangeratios were higher (P < 0.05) at 90 and 120 min of exercise for the SRO and SOF trials, respectively, than for the Con trial. At exhaustion, glucose, insulin, FFA, glycerol, epinephrine, and norepinephrine concentrations, respiratory exchange ratio, and muscle glycogen use in the vastus lateralis muscle weresimilar for all trials. Exercise time to exhaustion was 16% longer(P < 0.05) during the SRO thanduring the Con trial: 266.5 ± 13 and 225.1 ± 8 min,respectively. There was no difference in exercise time for the SOF(250.8 ± 12) and Con trials. We conclude that eating ameal with a high dietary fiber content and moderate glycemic index 45 min before prolonged moderately intense exercise significantly enhancesexercise capacity.

     

Effects of stirring and sparging on cultured hybridoma cells

The response of hybridoma cells to fluid shear caused by stirring and sparging has been investigated in a 2-L turbine-agitated bioreactor. Viable cell count, lactate dehydrogenase (LDH) release, and antibody secretion were measured over the course of batch culture experiments under varied conditions of stirring and gas sparging. The effectiveness of Pluronic F68 as a protective agent in sparged cultures was also studied. Growth was found to be unaffected by stirring of the culture under surface aerated conditions, but gas sparging had a significant detrimental effect on growth and antibody production. The effect of sparging was reduced when cultures were supplemented with Pluronic at a level of 0.4% (w/v). Experimental data were analyzed through formulation of models for LDH release and antibody production. Rates of cell lysis could be estimated by correlating extracellular LDH levels through the model for LDH release. The lysis rate estimated for sparged conditions was sufficiently large to approximately account for the observed decrease in the specific growth rate of the culture. The presence of Pluronic apparently interfered with the LDH release mechanism, so precise estimation of lysis rates under these conditions was not possible. Sparging was found not to have a detrimental effect on antibody production in cultures without Pluronic added. Specific antibody production rates in cultures supplemented with Pluronic were about 25% higher than in sparged cultures without Pluronic added.