29
inhibited by zinc binding agents.
LADH has been shown to oxi-
dize vitamin A, and to reduce retinene and is probably identical to retinene reductase.
Zine exists in at least two fractions in blood serum:
34 per cent as firmly bound zinc and 66 per cent as loosely
bound zinc
(Vikhbladh,
1951).
The firmly bound zinc is con-
sidered to be characteristic of metalloproteins, whereas the
loosely bound zinc occurs as a metal-protein complex.
substance exhibits enzymic properties and Vallee
Neither
(1957) believes
that the loosely bound complex is involved in zinc transport.
The role of carbonic anhydrase in teleosteen fishes has
bean the subject of intensive investigation by Maetz (1956).
Carbonic anhydrase in fish takes part in the regulation of the
internal environment and of secretory activity such as the
secretion of chlorides by the gills and of gases in the swim
bladder.
These secretions are linked to basic physiologic
functions: conservation of an internal environment either more
dilute or more concentrated than the external environment and
the maintenance of hydrostatic equilibrium.
The inhibition of
the activity of the enzyme in the eyes of fish by injection of
parasulfamidobenzoic acid or diamox, brought about a signifi-
cant acidification of the vitreous humor and of retinal tissue,
indicating that carbonic anhydrase functions in the regulation