GO
EDWARD C. CANTINO AND JAMES S. LOVETT
question : what is the first detectable alteration induced by bicarbonate
in the developing cell? For this question, less satisfying though it is,
some precise answers are available.
During exponential growth of an RS cell, as compared to an OC cell,
(a) the exponential growth rate is depressed by 46% (Cantino and
Lovett, 1960); (b) the Q 02 drops precipitously (Cantino and Lovett,
1960); and (c) the rate of synthesis of internal, soluble polysaccharide,
relative to the total dry weight of the cell (i.e., a differential exponential
rate) is roughly doubled (Cantino and Goldstein, 1961).
The next question follows logically: relative to RS differentiation, do
these altered parameters represent causes or effects? Depression of the
rates of both growth and oxygen consumption can be induced by
environmental changes without, simultaneously, inducing RS formation ;
they appear, therefore, not to be the cause—at least, the sole cause—of
morphogenesis. They are clearly, however, effects induced by the
presence of bicarbonate.
Are these metabolic changes consistent with current notions (Cantino,
1961a) about the bicarbonate trigger mechanism? If (a) the tricarboxylic
acid cycle is rendered sluggish or inoperative by bicarbonate as the
concept calls for; and (b) since, in particular, the growing RS cell is
known to accumulate exponentially a reserve pool of polysaccharide
(Cantino and Goldstein, 1961); and while simultaneously (c) it does not
consume exogenous glucose (Cantino and Lovett, 1960), one might well
expect that oxygen consumption would decrease sharply. Indeed, not
only does this occur (Cantino and Lovett, 1960), but the correlation is
strengthened significantly by the nature of the quantitative data.
The Qo 2 of the RS cell, at the end of its exponential growth, has been
reduced to about one-tenth (Cantino and Lovett, 1960) of the Q 02 of the
spore from which it was derived. If oxygen consumption were dependent
solely upon the operation of the tricarboxylic acid cycle as a ratelimiting factor, one would expect that turnover of the cycle would have
to decrease to one-tenth its previous rate. In this connection, the
available analytical data show a significant correlation. During the
developmental period in question—starting with the spore and ending
with the RS cell at the end of its exponential phase of growth—the total
activity of the isocitric dehydrogenase per cell increases about 6,500-fold
(Lovett and Cantino, 1961) ; the cell increases in both weight and volume
to about the same degree. But, the enzyme system which immediately
follows it in the tricarboxylic acid cycle, ketoglutaric dehydrogenase,
increases only 650-fold ; that is, its total quantity per cell rises to only onetenth the level of the total isocitric dehydrogenase ! Thus, the 10-fold
reduction in oxygen consumption induced by bicarbonate, and the
corresponding 10-fold decrease in accumulation of total ketoglutaric
EDWARD C. CANTINO AND JAMES S. LOVETT
question : what is the first detectable alteration induced by bicarbonate
in the developing cell? For this question, less satisfying though it is,
some precise answers are available.
During exponential growth of an RS cell, as compared to an OC cell,
(a) the exponential growth rate is depressed by 46% (Cantino and
Lovett, 1960); (b) the Q 02 drops precipitously (Cantino and Lovett,
1960); and (c) the rate of synthesis of internal, soluble polysaccharide,
relative to the total dry weight of the cell (i.e., a differential exponential
rate) is roughly doubled (Cantino and Goldstein, 1961).
The next question follows logically: relative to RS differentiation, do
these altered parameters represent causes or effects? Depression of the
rates of both growth and oxygen consumption can be induced by
environmental changes without, simultaneously, inducing RS formation ;
they appear, therefore, not to be the cause—at least, the sole cause—of
morphogenesis. They are clearly, however, effects induced by the
presence of bicarbonate.
Are these metabolic changes consistent with current notions (Cantino,
1961a) about the bicarbonate trigger mechanism? If (a) the tricarboxylic
acid cycle is rendered sluggish or inoperative by bicarbonate as the
concept calls for; and (b) since, in particular, the growing RS cell is
known to accumulate exponentially a reserve pool of polysaccharide
(Cantino and Goldstein, 1961); and while simultaneously (c) it does not
consume exogenous glucose (Cantino and Lovett, 1960), one might well
expect that oxygen consumption would decrease sharply. Indeed, not
only does this occur (Cantino and Lovett, 1960), but the correlation is
strengthened significantly by the nature of the quantitative data.
The Qo 2 of the RS cell, at the end of its exponential growth, has been
reduced to about one-tenth (Cantino and Lovett, 1960) of the Q 02 of the
spore from which it was derived. If oxygen consumption were dependent
solely upon the operation of the tricarboxylic acid cycle as a ratelimiting factor, one would expect that turnover of the cycle would have
to decrease to one-tenth its previous rate. In this connection, the
available analytical data show a significant correlation. During the
developmental period in question—starting with the spore and ending
with the RS cell at the end of its exponential phase of growth—the total
activity of the isocitric dehydrogenase per cell increases about 6,500-fold
(Lovett and Cantino, 1961) ; the cell increases in both weight and volume
to about the same degree. But, the enzyme system which immediately
follows it in the tricarboxylic acid cycle, ketoglutaric dehydrogenase,
increases only 650-fold ; that is, its total quantity per cell rises to only onetenth the level of the total isocitric dehydrogenase ! Thus, the 10-fold
reduction in oxygen consumption induced by bicarbonate, and the
corresponding 10-fold decrease in accumulation of total ketoglutaric