21
It would,
consequently be expected to scavenge positive ions.
3.132
Concentration in biological systems.
Many of
the bivalent metals of the transition series which occur in
only trace amounts in the sea exhibit remarkable biological
specificity and are concentrated in certain biological systems.
These elements exhibit a strong tendency to form coordination
complexes with organic functional groups, or ligands, having
one or more electron pairs available for the formation of coor-
dinate bonds.
Protein structure offers a variety of sites for
the formation of metal~protein coordinate bonds exemplified by
metallo-enzymes and the metal-porphyrin serum proteins.
to their incorporation into protein structure,
Prior
trace elements
must be collected by marine organisms from dilute solution or
dispersed suspension in the sea.
Harvey
(1955) proposed one
or more of three mechanisms by which this might come about:
(1)
adsorption of ions on cell-water interfaces,
(2)
absorp-
tion through semi-permeable membranes into the body fluids,
and
(3) the attachment of colloidal particles to which trace
metal ions are adsorbed to external mucous coatings of aquatic
Organisms.
The first two provide a pathway into marine organ-
isms for substances dissolved in sea water,
and the third
mechanism provides a means of concentrating the dispersed particulate matter suspended in it.