98
presented in Figure 9.
It shows the routes of entry and loss,
and the cycling of zine through the various organ systems of
the fish.
Major pathways are indicated by heavy lines.
Zinc
associated with particulate matter is taken in largely through
the mouth,
dissolved in the acid environment of the upper
digestive tract and absorbed through the gut into the
blood.
Dissolved zinc is taken in, principally through the gills,
directly into the blood.
In the blood,
zinc is associated with
(1) a protein carrier to which it is loosely bound,
(2) carbonic
anhydrase in the erythrocytes to which it is firmly bound,
and
(3) possibly to a leucocyte protein which binds it firmly and
which has been identified as a zinc protein in humans.
blood it is carried to the various tissues,
tein carrier or as carbonic anhydrase.
From the
either with the pro-
The loosely bound zinc
on the carrier is available for the manufacture of zinc enzymes
reguired for the metabolism of specific tissue components,
the carbonic anhydrase is available for its
and
predominant role
in COy transport and for the regulation of pH.
Specific enzymes
with which zine has been identified in vertebrates are listed in
the figure with the tissues with which they are associated.
Much of this information was derived from studies of vertebrates
other than fish.
However,
the biochemical reactions involving
the metabolism of living organisms in all their diversity, are