d-Alanine metabolism in the lucinid clam Lucinoma aequizonata |
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Authors: | S Wiley H Felbeck |
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Institution: | (1) Scripps Institution of Oceanography 0202, University of California San Diego, 92093-0202 La Jolla, CA, USA;(2) Samuel Lunenfeld Research Institute, Mount Sinai Hospital, 600 University Avenue, Rm 875, M5G 1X5 Toronto, Ontario, Canada |
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Abstract: | The chemoautotrophic symbiont-bearing clam Lucinoma aequizonata contains very high levels of free d-alanine in all tissues. The possible sources for this amino acid and its involvement in the clams' metabolism were investigated. Very low levels of d-alanine (generally below 1 mol·l-1) were measured in the sediment porewaters from the habitat of the clams. Experiments with 14C-labeled tracers demonstrate an active metabolism of d-alanine in the clams rather than a role as inert waste product. d-alanine is metabolized at about 0.12 mol·g fw-1·h-1. Label from aspartate, but not glucose and CO2, is incorporated into d-alanine. Incubation with labeled d-alanine did not result in formation of radioactive l-alanine. Tests for alanine racemase (EC 5.1.1.1) and d-amino acid oxidase (EC 1.4.3.3.) did not show activity in either gill, i.e. symbiont and host, or foot tissue. d-Alanine amino transferase (EC 2.6.1.b.) was demonstrated in gill and foot tissues. Two sources for d-alanine are proposed: a degradation of cell walls of symbiotic bacteria and production by the host using a d-specific alanine transaminase.Abbreviations aa
amino acid(s)
- fw
fresh weight
- HPLC
high-performance liquid chromatography
- MBH
methyl benzethonium hydroxyde
- NAC
N-acetyl-l-cysteine
- OPA
ortho-phthaldialdehyde
- TCA
tricarbonic acid |
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Keywords: | d-Alanine" target="_blank">d-Alanine Chemoautotrophic symbiosis Lucinidae Clam Lucinoma |
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