L'"lodel for Sustained Rhythmic Binary Logic
43
zero ("off") or very nearly 16 ("on"). The transformation from "off" to
"on" or vice-versa occurs in a time interval that is short compared to the
period of the rhythm.
At present it is a matter of speculation whether and to what extent such
rhythmic step-functions playa role in biological processes. A possible role
merits consideration however, since the main components of the model,
enzymes which exhibit a sigmoid relationship between activity and substrate concentration and multi-enzyme systems which experience feedback
product inhibition, are now well known. It is not unreasonable to expect
that if a model like the one described above is useful, it could be readily
provided by natural selection.
Acknowledgement
This work was supported in part by the National Science Foundation, grant
GB 3625.
References
1. MONOD, J., ]. WYMAN and J. CHANGEUX: ]. Mol. BioI. 12, 88 (1965).
2. MORALES, M., and D. McKAY: Biophys.]. 7,441 (1967).
3. WALTER, CH., R. PARKER and M. YeAS: ]. Theor. BioI. 15, 208 (1967).
4. YATES, R. A., and A. B. PARDEE: ]. BioI. Chern. 221, 757 (1956).
DisCtlssion
BETZ:
You certainly know the model proposed by HIGGINS to explain glycolytic
oscillations which is based on PFK being inhibited by its substrate A TP and
activated by the product FDP and by AMP, too, and, most efficiently, by
F-6-P. Would this model be able to produce such step functions as yours does?
WALTER:
Any system describable by the VOLTERRA equations possesses the potential
for oscillation. Although these models are considerably more complex than the
YATES-PARDEE scheme (they require positive feedback) they could be used in
place of pathway A in scheme I. In fact, the source of the oscillatory character
is irrelevant (WALTER, C. R. PARKER and M. YeAs: ]. Theor. BioI. 15, 208
(1967)).
BETZ:
In your model the existence of a net flux is not a sufficient condition for working as an oscillator or does it need some really irreversible enzymatic step?
WALTER:
If the n-1 chemical reactions of pathway A were at equilibrium I would not
expect the existence of a net flux to result in an oscillation. However, I do not
think the oscillations depend on literal irreversibility of the chemical reactions.
43
zero ("off") or very nearly 16 ("on"). The transformation from "off" to
"on" or vice-versa occurs in a time interval that is short compared to the
period of the rhythm.
At present it is a matter of speculation whether and to what extent such
rhythmic step-functions playa role in biological processes. A possible role
merits consideration however, since the main components of the model,
enzymes which exhibit a sigmoid relationship between activity and substrate concentration and multi-enzyme systems which experience feedback
product inhibition, are now well known. It is not unreasonable to expect
that if a model like the one described above is useful, it could be readily
provided by natural selection.
Acknowledgement
This work was supported in part by the National Science Foundation, grant
GB 3625.
References
1. MONOD, J., ]. WYMAN and J. CHANGEUX: ]. Mol. BioI. 12, 88 (1965).
2. MORALES, M., and D. McKAY: Biophys.]. 7,441 (1967).
3. WALTER, CH., R. PARKER and M. YeAS: ]. Theor. BioI. 15, 208 (1967).
4. YATES, R. A., and A. B. PARDEE: ]. BioI. Chern. 221, 757 (1956).
DisCtlssion
BETZ:
You certainly know the model proposed by HIGGINS to explain glycolytic
oscillations which is based on PFK being inhibited by its substrate A TP and
activated by the product FDP and by AMP, too, and, most efficiently, by
F-6-P. Would this model be able to produce such step functions as yours does?
WALTER:
Any system describable by the VOLTERRA equations possesses the potential
for oscillation. Although these models are considerably more complex than the
YATES-PARDEE scheme (they require positive feedback) they could be used in
place of pathway A in scheme I. In fact, the source of the oscillatory character
is irrelevant (WALTER, C. R. PARKER and M. YeAs: ]. Theor. BioI. 15, 208
(1967)).
BETZ:
In your model the existence of a net flux is not a sufficient condition for working as an oscillator or does it need some really irreversible enzymatic step?
WALTER:
If the n-1 chemical reactions of pathway A were at equilibrium I would not
expect the existence of a net flux to result in an oscillation. However, I do not
think the oscillations depend on literal irreversibility of the chemical reactions.