Regulation of the Calvin cycle for CO2 fixation as an example for general control mechanisms in metabolic cycles.

The theory of a metabolic cycle with the main portion of its intermediates remaining inside the cycle during one turnover has been developed. On this basis, the regulation of the Calvin cycle is analyzed. It is demonstrated that not only the reactions of non-equilibrium enzymes, as the carboxylation of ribulose 1,5-bisphosphate, but reactions that operate close to a thermodynamic equilibrium, especially the reduction of 3-phosphoglycerate and the transketolase reaction can significantly influence the total turnover period in the Calvin cycle. The role of compensating mechanisms in the maintenance of the photosynthesis rate upon changes of environmental conditions and of enzyme contents is analyzed for the Calvin cycle. It is shown that the change of the total quantity of the metabolites is one of the main self-regulated mechanisms in the Calvin cycle. A change of the ATP/ADP ratio can be used by the cell to maintain the CO2 assimilation rate, when the total quantity of the metabolites is changed. The developed analysis permits to explain some experimental data obtained with transgenic plants with restricted efflux of carbon from the chloroplasts.     

Rabbit immunoglobulin allotype A12: A new agglutinating specificity

A new allotype, A12, present on rabbit IgG is described. This allotype is detected by inhibition-of-agglutination techniques similar to those employed for the previously described allotype A11. The specificity is on the H chain in the hinge region of IgG. It can be associated with any of the H chain group a allotypes. A11 and A12 are transmitted by codominant autosomal genes.This work was supported by Welch Foundation Grant F 209, by grants AI 07184 and AI 07995 from the National Institute of Allergy and Infectious Diseases, and by an NIH Animal Care Grant FR 00433.Recipient of PHS Career Development Award 1-K3-GM-21,252.Supported by a City of Hope fund established in the name of Ralph Carson.     

Lettuce seed germination: A phytochrome-mediated increase in the growth rate of lettuce seed radicles

Summary The rate of straight growth in mannitol of the axial portion of 2 different samples of photosensitive lettuce seeds was followed after red and far-red irradiation. If the growing half-seeds were classified into proportions of the sample that had undergone a growth increment greater than a certain, selected value, growth rate was found to be enhanced by red light and this enhancement paralleled the phytochrome-mediated increase in the rate of appearance of a geotropic curvature in seed axes, an effect which had been previously reported. The increase in the rate of growth of the radicle by red light was limited to early growth. Once extension has exceeded a certain value the rate of further growth is independent of the state of phytochrome.     

Locomotor performance and cost of transport in the northern flying squirrelGlaucomys sabrinus

We assess locomotor performance by northern flying squirrelsGlaucomys sabrinus Shaw, 1801 and test the hypothesis that gliding locomotion is energetically cheaper than quadrupedal locomotion. We measured 168 glides by 82 northern flying squirrels in Alaska. Mean glide distances varied from 12.46 m to 14.39 m, with a maximum observed glide distance of 65 m. Mean glide angles varied from 41.31° to 36.31°, and mean air speed ranged from 6.26 m/s to 8.11 m/s. There were no differences in the performance of male and female flying squirrels. We used models of transport cost to provide an initial assessment of the hypothesis that gliding locomotion is energetically less expensive than quadrupedal locomotion. For glides of average length, cost of gliding was less than cost of quadrupedal locomotion except when the animals climbed to the launch point very slowly or ran quickly. Thus the hypothesis that gliding is less expensive than quadrupedal locomotion is supported.