A numerical model for the oxygenation of blood in lung capillaries--effect of nth order one-step kinetics of oxygen uptake by haemoglobin

A numerical model is described for the oxygenation of blood in lung capillaries by considering the transport mechanisms of molecular diffusion, convection and the facilitated diffusion due to the presence of haemoglobin. In order to represent the oxygen dissociation curve accurately in the model, the nth order one-step kinetics of oxygen uptake by haemoglobin has been used. The resulting system of coupled, non-linear partial differential equations is solved numerically. It is shown that the blood is required to traverse a larger distance in the capillary before becoming fully oxygenated with nth order one-step kinetics in comparison to first-order one-step kinetics.     

Possible explanation of the disparity between the in vitro and in vivo measurements of Rubisco activity: a study in loblolly pine grown in elevated pCO2.

Rubisco activity can be measured using gas exchange (in vivo) or using in vitro methods. Commonly in vitro methods yield activities that are less than those obtained in vivo. Rubisco activity was measured both in vivo and in vitro using a spectrophotometric technique in mature Pinus taeda L. (loblolly pine) trees grown using free-air CO2 enrichment in elevated (56 Pa) and current (36 Pa) pCO2. In addition, for studies where both in vivo and in vitro values of Rubisco activity were reported net CO2 uptake rate (A) was modelled based on the in vivo and in vitro values of Rubisco activity reported in the literature. Both the modelling exercise and the experimental data showed that the in vitro values of Rubisco activity were insufficient to account for the observed values of A. A trichloroacetic acid (TCA) precipitation of the protein from samples taken in parallel with those used for activity analysis was co-electrophoresed with the extract used for determining in vitro Rubisco activity. There was significantly more Rubisco present in the TCA precipitated samples, suggesting that the underestimation of Rubisco activity in vitro was attributable to an insufficient extraction of Rubisco protein prior to activity analysis. Correction of in vitro values to account for the under-represented Rubisco yielded mechanistically valid values for Rubisco activity. However, despite the low absolute values for Rubisco activity determined in vitro, the trends reported with CO2 treatment concurred with, and were of equal magnitude to, those observed in Rubisco activity measured in vivo.     

THE ZOOSPORE OF CHLOROKYBUS ATMOPHYTICUS,A CHAROPHYTE WITH SARCINOID GROWTH HABIT

Chlorokybus atmophyticus has a sarcinoid growth habit and produces scale-covered zoospores. Flagella are laterally inserted and attached internally to a multilayered structure characteristic of the Charophyceae. There are two kinds of pyrenoid in each cell, a feature previously observed in only one scaly green flagellate. C. atmophyticus demonstrates that the sarcinoid growth habit arose independently at least twice in the green algae and cannot be used to define taxonomic groups unless combined with other criteria. It is further concluded that C. atmophyticus should be classified in a separate family Chlorokybaceae and a separate order Chloroky bales.     

Effect of 3T3 plasma membranes on cells exposed to epidermal growth factor

Epidermal growth factor (EGF) induced DNA synthesis in non-confluent, G₀-arrested Swiss 3T3 fibroblasts is partially blocked by plasma membranes isolated from the EGF receptor deficient NR-6 Swiss 3T3 cell line. This inhibition could be due to either a steric block of the receptor by the membranes, a membrane induced down regulation of the EGF receptor, or a signal generated by membrane binding which is antagonistic towards the mitogenic signal generated by EGF. Binding measurements utilizing ¹²⁵I-labeled EGF demonstrated that membranes do not block either the EGF induced down regulation of the receptor or alter the number of receptors on the surface. These results suggest that the membranes exert their inhibitory effect via generation of a signal which is antagonistic to the EGF induced mitogenic signal, with the result expressed as a reduced mitogenic response.