UPTAKE AND UTILIZATION OF DISSOLVED GLYCINE BY AURELIA AURITA SCYPHISTOMAE: TEMPERATURE EFFECTS ON THE UPTAKE PROCESS; NUTRITIONAL ROLE OF DISSOLVED AMINO ACIDS
J. MALCOLM SHICK 1
1 Department of Biology, Texas A & M University, College Station, Texas
1. The temperature sensitivity of glycine uptake by Aurelia aurita scyphistomae from Corpus Christi, Texas is similar to that of other rate processes in warm-temperate zone scyphozoans.
2. Both Texas polyps and those from the York River, Virginia show inverse temperature compensation of glycine uptake; the phenomenon is therefore apparently not latitudinally based.
3. The values of Kt and Vmax for glycine uptake are directly related to temperature between 12° and 32° C. The increasing affinity of the glycine uptake system with decreasing temperature may be analogous to "positive thermal modulation" of enzyme-substrate affinity in poikilotherms.
4. The fivefold increase in Kt between 12° and 32° C indicates that environmental temperature is an important consideration in intra- and interspecific comparisons of the affinities of amino acid uptake systems in marine invertebrates.
5. Eight weeks of food deprivation at 20° C result in a 77.5% reduction in the number of polyps strobilating in response to temperature increase and exposure to iodide. This effect can be abolished by exposing starved polyps to environmental concentrations of glycine or alanine during the starvation period.
6. Exposure of starved polyps to dissolved glucose during the 8-week period also overrides the diminution of the strobilation response. However, starved and starved/glucose-exposed polyps produce a higher percentage of abnormal ephyrae than do fed and starved/amino acid-exposed polyps, emphasizing the importance of dissolved amino acids as nitrogen sources.
7. All starved polyps, whether or not they are exposed to dissolved organic compounds, cease budding after 14-15 days of food deprivation.
8. Oxygen consumption declines to 25.9% of the value in fed polyps during 2 weeks of food deprivation. Exposure of starved polyps to dissolved glycine produces an increase in this parameter.
9. There is no effect of 2 weeks of food deprivation on glycine uptake by polyps. However, starvation does produce an enhanced rate of glycine catabolism, due in part to the increased production of CO2 from the alpha carbon of the molecule. The predominance of glycine among amino acids dissolved in seawater, and its increased oxidation during starvation, may enhance its importance as a supplemental energy source for marine invertebrates.
10. The internal pool concentrations of most free amino acids decline during 2 weeks of food deprivation; the total FAA concentration of the pools is little affected, largely due to compensatory increases in glycine, taurine and -alanine.
http://www.biolbull.org/cgi/content/abstract/148/1/117
