Starvation steady-state

The activity of carbamoyl phosphate synthase I is determined by A -acetylglutamate, whose steady-state level is dictated by its rate of synthesis from acetyl-CoA and glutamate and its rate of hydrolysis to acetate and glutamate. These reactions are catalyzed by A -acetylglu-tamate synthase and A -acetylglutamate hydrolase, respectively. Major changes in diet can increase the concentrations of individual urea cycle enzymes 10-fold to 20-fold. Starvation, for example, elevates enzyme levels, presumably to cope with the increased production... 

Fig. 7.4. Developmental path for the mechanism of intercellular communication by cAMP signals in D. discoideum, in agreement with the variations observed for the activity of adenylate cyclase and phosphodiesterase after starvation. The diagram is constructed as indicated in fig. 7.2, for system (5.1) to which the term (-k a) has been added in the evolution equation for variable a, to take into account the utilization of ATP to ends other than cAMP synthesis. In these conditions, the developmental path accounting for the sequential transitions of fig. 7.1 corresponds to the increase in the two enzyme activities that is observed in the hours that follow starvation (fig. 7.3). Domains A, B and C have the same meaning as in fig. 7.2 domain D corresponds to a stable steady state characterized by an elevated level of cAMP, while two stable steady states can coexist in E. The signal considered for amplification in B is y = 10. Parameter values are V = 0.04 s, k, - 0.4 s k = 10" s", = 10, L = lO", q = 100 (Goldbeter Segel, 1980).

After 3 days of starvation, whole-body metabolism reaches a new steady state, as depicted in Fig. 13-18. The long-term problem for siavival is the incessant loss of total protein mass. 

Fig. 13-18 Major metabolic interorgan fuel flow during established steady-state starvation. Amino acids are indicated by aa, fatty acids by FA, and ketone bodies by KB.

How long can a steady state of protein degradation be maintained during starvation ... 

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