184
ERNEST SCHOFFENIELS
aspect is always considered when one studies the effect of alkaline earth
on cellular functions. One has thus a biological classification of the
cations corresponding to the periodic table of elements. This classification is also found if one considers the effect of cations on enzymatic
reactions. It is observed that alkaline earths are fixed more or less firmly
to the enzyme and often bind the substrate to the enzyme in the formation of the Michaelis-Menten complex, while alkali metal ions influence
the reaction in a way not clearly understood. They do not form covalent
bond or coordinate linkage. They may change the charge density at the
surface of the enzyme affected by these cations. Schematically one may
therefore say that the alkaline earths would play an essential role as
fundamental elements in the molecular architecture of the cell while
the alkali metal ions would be more directly related to phenomena
involving the liquid phases of biological systems (see, however, Section
VIII).
If this classification seems indeed to correspond to many observations,
it is, however, not an absolute one, as within certain limits, fixation of
alkaline earth are directly related to the presence of alkali metal ions. We
may summarize our view in the following way. (a) Cellular structures
are able to bind not only alkaline metal ions but also alkaline earths.
(b) The various cations bound to the structure must be in a well-defined
ratio if the functional integrity of the structure is to be optimum.
(c) There is "competition"* between various cations for the cellular
structures.
A. PASSIVE PERMEABILITY
As shown above the electrical potential difference existing between
the intracellular fluid and the extracellular space is due to the passive
permeability characteristics of the membrane as well as the unequal
distribution of ions between the two liquid phases. The unequal distribution of ions is the result of an active transport mechanism (mainly Na
and K) requiring metabolic energy.
The molecular architectures responsible for the various permeability
characteristics are differently affected not only by metabolic inhibitors
but also by the ionic composition of the surrounding fluids, as shown by
the following examples.
1. Action of Calcium on Membrane Rectification
The potential difference existing spontaneously across the giant axon
membrane can be varied by passing an electrical current across it (177,
* No experimental evidence is available so far to decide whether or not we are
dealing with a true competition as defined in enzymology.
ERNEST SCHOFFENIELS
aspect is always considered when one studies the effect of alkaline earth
on cellular functions. One has thus a biological classification of the
cations corresponding to the periodic table of elements. This classification is also found if one considers the effect of cations on enzymatic
reactions. It is observed that alkaline earths are fixed more or less firmly
to the enzyme and often bind the substrate to the enzyme in the formation of the Michaelis-Menten complex, while alkali metal ions influence
the reaction in a way not clearly understood. They do not form covalent
bond or coordinate linkage. They may change the charge density at the
surface of the enzyme affected by these cations. Schematically one may
therefore say that the alkaline earths would play an essential role as
fundamental elements in the molecular architecture of the cell while
the alkali metal ions would be more directly related to phenomena
involving the liquid phases of biological systems (see, however, Section
VIII).
If this classification seems indeed to correspond to many observations,
it is, however, not an absolute one, as within certain limits, fixation of
alkaline earth are directly related to the presence of alkali metal ions. We
may summarize our view in the following way. (a) Cellular structures
are able to bind not only alkaline metal ions but also alkaline earths.
(b) The various cations bound to the structure must be in a well-defined
ratio if the functional integrity of the structure is to be optimum.
(c) There is "competition"* between various cations for the cellular
structures.
A. PASSIVE PERMEABILITY
As shown above the electrical potential difference existing between
the intracellular fluid and the extracellular space is due to the passive
permeability characteristics of the membrane as well as the unequal
distribution of ions between the two liquid phases. The unequal distribution of ions is the result of an active transport mechanism (mainly Na
and K) requiring metabolic energy.
The molecular architectures responsible for the various permeability
characteristics are differently affected not only by metabolic inhibitors
but also by the ionic composition of the surrounding fluids, as shown by
the following examples.
1. Action of Calcium on Membrane Rectification
The potential difference existing spontaneously across the giant axon
membrane can be varied by passing an electrical current across it (177,
* No experimental evidence is available so far to decide whether or not we are
dealing with a true competition as defined in enzymology.