4. ENERGY-RICH COMPOUNDS
133
of ADP to ATP, according to Reaction 41. In contrast to Reaction 39,
this process did not require a primer.
nADP + (P0 3 ) n ^ nATP
(41)
ADP could not be replaced by the diphosphates of cytidine, uridine, or
guanosine, or by AMP.
Polyphosphate synthesis according to Reaction 41 was also demonstrated in extracts of Corynebacterium diphtheriae (140). This result is
not unexpected since this organism has long been known to accumulate
large amounts [approx. 30% of the cell weight (141)] of "volutin."
The mechanism of polyphosphate synthesis in cells of higher plants
(109) and algae (142) has not been investigated. However, the formation of maximum amounts of polyphosphate in Chlorella (142) was
found to occur in the light and in the absence of ATP-utilizing reactions such as C0 2 fixation; in the dark, the amount of polyphosphate
was decreased. It is possible that polyphosphates are formed in plant
cells by a reaction similar to Eqs. 39 or 41.
Nickerson (143) found that yeasts are able to polymerize glucose
and phosphate at the same rate and that both polymerizations are inhibited to the same extent by addition of dinitrophenol and azide. Reaction 42 was proposed as a
n(Glucose-l-phosphate) ^ Glycogen + (P0 3 )n
(42)
mechanism for polyphosphate formation on the assumption that the
insolubility of the polyphosphate product would shift the otherwise
unfavorable equilibrium.
c. Function. Changes in content of the insoluble polyphosphate pool
during nucleic acid synthesis (115-117, 128b, 134r-135c) and cell division (132, 134, 135) suggest that these compounds function as phosphate reservoirs; release of Pi could be effected by the action of specific
depolymerizing enzymes. Such enzymes have been found in yeasts
(122), in animal tissues (123), in serum (144), in molds (145, 146), in
plants (146a), and in bacteria (110, 127, 140, 146, 146b). Enzymes
capable of hydrolyzing tripolyphosphate, trimetaphosphate and tetrametaphosphate are also found in these tissues and cells (109, 146c),
and pyrophosphatase (147) has been found in almost all tissues.
The "energy-rich" nature of polyphosphates was first established by
Meyerhof's group (40) from measurements of the AF and ΔΗ for the
hydrolysis of metaphosphate. It is obvious that Reactions 39 and 41
provide a means for mobilizing polyphosphate for energy purposes; for
example, ATP synthesis via these reactions has been coupled to the
phosphorylation of glucose (140) and glycerol (148). Under unfavorable growth conditions, or at certain stages in the growth cycle, the
133
of ADP to ATP, according to Reaction 41. In contrast to Reaction 39,
this process did not require a primer.
nADP + (P0 3 ) n ^ nATP
(41)
ADP could not be replaced by the diphosphates of cytidine, uridine, or
guanosine, or by AMP.
Polyphosphate synthesis according to Reaction 41 was also demonstrated in extracts of Corynebacterium diphtheriae (140). This result is
not unexpected since this organism has long been known to accumulate
large amounts [approx. 30% of the cell weight (141)] of "volutin."
The mechanism of polyphosphate synthesis in cells of higher plants
(109) and algae (142) has not been investigated. However, the formation of maximum amounts of polyphosphate in Chlorella (142) was
found to occur in the light and in the absence of ATP-utilizing reactions such as C0 2 fixation; in the dark, the amount of polyphosphate
was decreased. It is possible that polyphosphates are formed in plant
cells by a reaction similar to Eqs. 39 or 41.
Nickerson (143) found that yeasts are able to polymerize glucose
and phosphate at the same rate and that both polymerizations are inhibited to the same extent by addition of dinitrophenol and azide. Reaction 42 was proposed as a
n(Glucose-l-phosphate) ^ Glycogen + (P0 3 )n
(42)
mechanism for polyphosphate formation on the assumption that the
insolubility of the polyphosphate product would shift the otherwise
unfavorable equilibrium.
c. Function. Changes in content of the insoluble polyphosphate pool
during nucleic acid synthesis (115-117, 128b, 134r-135c) and cell division (132, 134, 135) suggest that these compounds function as phosphate reservoirs; release of Pi could be effected by the action of specific
depolymerizing enzymes. Such enzymes have been found in yeasts
(122), in animal tissues (123), in serum (144), in molds (145, 146), in
plants (146a), and in bacteria (110, 127, 140, 146, 146b). Enzymes
capable of hydrolyzing tripolyphosphate, trimetaphosphate and tetrametaphosphate are also found in these tissues and cells (109, 146c),
and pyrophosphatase (147) has been found in almost all tissues.
The "energy-rich" nature of polyphosphates was first established by
Meyerhof's group (40) from measurements of the AF and ΔΗ for the
hydrolysis of metaphosphate. It is obvious that Reactions 39 and 41
provide a means for mobilizing polyphosphate for energy purposes; for
example, ATP synthesis via these reactions has been coupled to the
phosphorylation of glucose (140) and glycerol (148). Under unfavorable growth conditions, or at certain stages in the growth cycle, the