Effect of Partial Medium Replacement on Cell Growth and Protein Production for the High-Five™ insect cell line

The potential of spent medium to support the growth and recombinant protein production of High-Five? cells was investigated. Growth in medium consisting of three parts fresh and one part spent medium was comparable to that in fresh medium (maximal specific growth rates of 0.028 and 0.029 h^?1, and maximal cell densities of 4 and 4.5 × 10⁶ cells ml^?1, respectively). Glucose exhaustion coincided with an abrupt decrease of viability. Of 15 amino acids analyzed, not a single one was completely exhausted at the end of the growth phase. Growth in medium consisting of equal parts spent and fresh medium led to lower maximal cell concentration (2.9 × 10⁶ cells ml^?1) with a smoother death phase. Glucose supplementation at the beginning of the culture or at the end of the growth phase did not lead to an increase of either the maximal cell density or the specific growth rate. Infection of High-Five? cells at three different densities (1.4, 2.5 and 4.2 × 10⁶ cells ml^?1) without medium change led to monotonically decreased specific productions for β-galactosidase. Partial (75%) or total medium replacement at the higher infection density restored the specific production at the levels of the intermediate density infection (321, 292 and 389 U.(10⁶ cells)^?1, respectively).     

Diel patterns of zooplankton grazing in a shallow lake

A diel survey of in situ species-specific zooplankton clearancerates (with radioactively labelled Chlorella cells) was conductedin the shallow lake of Cr?teil characterized by small-sizedplanktonic forms (algae<10µm and zooplankton <1.3mm). Experiments were performed every 4h at two depths (1 and4m). Power functions relating individual filtering rates tobody length were established for the three most abundant cladoceransand for calanoids (nauplii being included in this feeding group),for each depth and time. No filtering penodicity was observedin Ceriodaphnia spp., adults and copepodites of Eudiaptomusgracilis and Eurytemora velox, and nauplii. On the contrary,clear nocturnal filtering peaks were obtained for Daphnia spp.and for Diaphanosoma brachyurum, these being more pronouncedfor the larger individuals at 1 m deep. The observed diel periodicitycannot be explained by variations in physico-chemical parametersor food concentration alone. The ecological significance ofthis phenomenon in the polymictic lake of Cr?teil is discussedin the light of previously published data and the hypothesesaccounting for it.     

Effect of NAD on flounder muscle glyceraldehyde 3-phosphate dehydrogenase

Flounder muscle (Pseudopleuronectes americanus) glyceraldehyde-3-phosphate dehydrogenase was characterized as to its stability towards various inactivating treatments in the presence and absence of the enzyme cofactor, NAD. Incubation of a partially purified enzyme preparation at urea concentrations greater than 2 M produced a very rapid inactivation. NAD greatly reduced the rate of inactivation at all the urea concentrations tested. Incubation of each of the three major muscle enzyme forms in 0.1 percent trypsin or chymotrypsin for forty-five minutes decreased the activity of each form by 65 percent and 55 percent, respectively. NAD (5mM) afforded complete protection to each enzyme form from proteolytic digestion by these two enzymes. Exposure of each form to 50 degrees or 20 mM ATP also led to gross inactivation which could be greatly reduced if the respective incubations were performed in the presence of 5mM NAD. NAD was also found to be required for the renaturation of the unfolded urea-denatured subunits to form the active tetramer.