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Amino Acids

Amino acids (AA) are in general any organic compounds containing carboxylic (-C00H) and amine (-NH2) functional groups. From among vast number of AAs, most important are L-alpha-amino acids - headstones of all proteins and thus key in natural sciences.


Version 2012-III

Amino Acids

Amino acids

Amino acids (AA) are in general any organic compounds containing carboxylic (-C00H) and amine (-NH2) functional groups. From among vast number of AAs, most important are L-alpha-amino acids - headstones of all proteins and thus key in natural sciences.

The basic characteristics of AA

Aliphatic
chain
structure
Particular AA is defined by the structure of side aliphatic chain (the R in molecule picture) determining its major properties.
Chirality
All alpha-AA but glycine occurs in two mirror forms (L and D optical isomers - antipodes). With few exceptions L-isomers vastly prevail in proteins formation.
Hybridism
As AA contain both carboxylic and amine group, they are both acid and base at the same time. This fact is important for AA polar solution (in water for instance) and key role plays pH value.
At certain pH value (AA-specific) the negative and positive charges of functional groups are equal and molecule acts as neutral one. Under described conditions – isoelectric point – the molecule is called Zwitterion (from German Zwitter - hybrid) and has very low solubility and could be often isolated from solution as precipitate.

Biogennous role

The AA could be metabolized in following ways by living organisms:

  • Growth - peptide and protein synthesis
  • Functionality - formation of non-protein molecules
  • Gaining energy by oxidation of AA

Essential and non-essential AA can be defined from the point of view of particular living organism. Essential are those AA, which could be synthesised inside the organisms body and the only source to obtain them is a food or – in case of corals for instance – seawater.

Growth – peptide and protein synthesis

Protein synthesis is in fact a kind of polymerization, where various AA reacts and forms molecular chain via Peptide bond:

Peptide Bond

Reaction needs an energy supply and is not occurring directly. Entire process is determined by genetic code and mediated by RNA or in smaller extent by enzymes. Resulting protein is defined by the sequence and number of particular AA.

Functionality – non-protein molecules synthesis

AA acts here as the precursors of important non-protein molecules, such as neurotransmitters, porphyrins, nucleotides, hormones etc. Some marine animals, for example cone snails, are able to convert L-isomers of AA to D-isomers, which acts against other organisms as violent poisons and thus are perfect anti-predator weapons. Even the only difference between isomers is a mirror structure, biological effect is dramatically dissimilar.

Utilisation of free amino acids

Rate of AA adsorption by invertebrates

There are following AA resources for marine invertebrates available:

  • Self-synthesis
  • Particulate organic food
  • Seawater

Natural seawater contains smaller amount of free dissolved AA and their direct biological utilisation has been studied among many marine invertebrates with relatively definite results valid for absolute majority of investigated subjects:

Marine organisms adsorb free AA from seawater rapidly and in substantial amount

Graph shows the rate of selected AA adsorption by sea mollusc Spinula solidissima during 24-hours exposure in % of initial AA concentration:

 
Graph I

Following table shows average rate of selected AA adsorption by particular groups of animals after 16 - 24-hours exposure in % of initial AA concentration. Adsorption rates correspond to the way of food uptake and are significant especially for seawater-filter feeders.

Sponges
64%
Sipunculidae (peanut worms)
36%
Cnidarians
34%
Moluscs
47%
Ribbonlike worms
58%
Arthropods (e.g. barnacles)
1%
Bryozoans (moss animals)
70%
Echinoderms (e.g. starfish)
64%
Annelids (segmented worms)
57%
Chordates (e.g. sea squirt)
32%

AA-impact on symbiosis of corals and Zooxanthellae

Large number of Anthozoans (sea anemones and corals) harbours in their cells symbiotic dinoflagellates - Zooxanthellae. Symbiotic coexistence lies in linked metabolism of carbon, nitrogen and phosphorus above all:

  • Zooxanthellae provide their hosts
    - in the form of carbon compound as the products of photosynthesis - with:
    • Up to 90% of its total energy budget
    • Substances needed for growth
  • Hosts provides Zooxanthellae with:
    • Living space and shelter
    • Nutrition
      - in fact waste metabolic products containing phosphorus and nitrogen
    • Continuous CO2 (carbon dioxide) supply for photosynthesis

A question for scientific research is what hosts chemical factor initializes and controls the process of photosynthetic products release from the cells of Zooxanthellae to those of hosts. One of related scientific works investigated this problem on Pocillopora damicornis coral species. A set of free amino acids has been determined as a host factor, which:

  • initializes selective release of photosynthetic products for hosts needs
  • increases the ability of carbon fixation by Zooxanthellae

It has been found the free AA plays important role of signal molecules for biologic processes.

Literature

UPTAKE OF AMINO ACIDS BY MARINE INVERTEBRATES, Grover C. Stephens and Robert A, Schinslw University of Minnesota and Marinc Biological Laboratory, Woods Hole, Massachusetts.
Free amino acids exhibit anthozoan "host factor" activity: They induce the release of photosynthate from symbiotic dinoflagellates in vitro RuTH D. GATES*t, OVE HOEGH-GULDBERGt, MARGARET J. MCFALL-NGAI§, KARL Y. BIL'*, AND LEONARD MUSCATINE* *Biology Department, University of California, Los Angeles, 405 Hilgard Avenue, Los Angeles, CA 90024-1606; *Department of Biological Sciences, University of Sydney, Sydney, New South Wales 2006, Australia; and §Department of Biological Sciences, University of Southern California, Los Angeles, CA 90089-0371

 
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