134
F. M. HUENNEKENS AND H. R. WHITELEY
accumulation of ATP might give rise to polyphosphate via the abov
reactions. Such an accumulation of polyphosphate has been observe»
frequently (115, 118, 128b, 134-136, 142, 148-150b). Upon resumptio
of growth, ATP utilization would yield ADP, which could then be re
cycled to ATP by reversal of Reaction 39 or 41. The function of pol)
phosphates would thus be analogous to that of the N-phosphate coir
pounds, phosphocreatine and phosphoarginine, in animal tissues. It is c
interest to note that cells capable of accumulating large amounts c
polyphosphate—i.e., yeasts, molds, plant cells, and bacteria—do nc
contain the N-phosphate compounds.
The "energy-rich" bond of pyrophosphate could also be preserve»
through the concerted action (50) of the enzymes mediating Reaction
39 and 40. Summation of these equations yields the net reaction (Ec
43):
PP + ADP ^± P* + ATP
(4i
Some evidence has been obtained (50) that a single enzyme, adenylat
kinase, can bring about Reaction 43.
As stated earlier, some tissues are able to carry out Reaction 3
thus conserving the "energy-rich" bond of tripolyphosphate; the rate c
this reaction, however, is very low. Although the affinity of myosin fc
tripolyphosphate is poor (151), this compound can cause a sligr
contraction of myofibrils (152). No evidence has been obtained for th
participation of other low molecular weight polyphosphates as "energy
rich" reservoirs.
Polyphosphates may also function to control cellular metabolisr
(118, 135a, 136, 153) by virtue of their ability to complex with cation
and proteins (125,126). Inactivation or removal of essential enzymes, c
binding of cations required for enzyme activation, would obviously in
fluence the course of metabolism. It has been shown (154), for example
that metaphosphate inhibits hexokinase both in vivo and in vitro b
virtue of its ability to bind Mg
2+ .
d. Distribution. Schmidt (109) has reviewed the occurrence c
polyphosphates in yeasts, plant cells, molds, and many bacteria. Asid
from pyrophosphate, and possibly small amounts of tripolyphosphat
formed via Reaction 38, polyphosphates have not been found in ani
mals with the exception noted below. This is surprising in view of th
widespread distribution in animal tissues of enzymes capable of de
polymerizing polyphosphates (123, 144).
Niemerko and co-workers (155-157) found that 2-4$ of the excret
of the larvae of the wax moths Galleria mellonella and Achroia grisell
consists of polyphosphate. These observations have been confirmed anc
F. M. HUENNEKENS AND H. R. WHITELEY
accumulation of ATP might give rise to polyphosphate via the abov
reactions. Such an accumulation of polyphosphate has been observe»
frequently (115, 118, 128b, 134-136, 142, 148-150b). Upon resumptio
of growth, ATP utilization would yield ADP, which could then be re
cycled to ATP by reversal of Reaction 39 or 41. The function of pol)
phosphates would thus be analogous to that of the N-phosphate coir
pounds, phosphocreatine and phosphoarginine, in animal tissues. It is c
interest to note that cells capable of accumulating large amounts c
polyphosphate—i.e., yeasts, molds, plant cells, and bacteria—do nc
contain the N-phosphate compounds.
The "energy-rich" bond of pyrophosphate could also be preserve»
through the concerted action (50) of the enzymes mediating Reaction
39 and 40. Summation of these equations yields the net reaction (Ec
43):
PP + ADP ^± P* + ATP
(4i
Some evidence has been obtained (50) that a single enzyme, adenylat
kinase, can bring about Reaction 43.
As stated earlier, some tissues are able to carry out Reaction 3
thus conserving the "energy-rich" bond of tripolyphosphate; the rate c
this reaction, however, is very low. Although the affinity of myosin fc
tripolyphosphate is poor (151), this compound can cause a sligr
contraction of myofibrils (152). No evidence has been obtained for th
participation of other low molecular weight polyphosphates as "energy
rich" reservoirs.
Polyphosphates may also function to control cellular metabolisr
(118, 135a, 136, 153) by virtue of their ability to complex with cation
and proteins (125,126). Inactivation or removal of essential enzymes, c
binding of cations required for enzyme activation, would obviously in
fluence the course of metabolism. It has been shown (154), for example
that metaphosphate inhibits hexokinase both in vivo and in vitro b
virtue of its ability to bind Mg
2+ .
d. Distribution. Schmidt (109) has reviewed the occurrence c
polyphosphates in yeasts, plant cells, molds, and many bacteria. Asid
from pyrophosphate, and possibly small amounts of tripolyphosphat
formed via Reaction 38, polyphosphates have not been found in ani
mals with the exception noted below. This is surprising in view of th
widespread distribution in animal tissues of enzymes capable of de
polymerizing polyphosphates (123, 144).
Niemerko and co-workers (155-157) found that 2-4$ of the excret
of the larvae of the wax moths Galleria mellonella and Achroia grisell
consists of polyphosphate. These observations have been confirmed anc