Meeting Abstract
Dietary restriction (DR), reducing feeding without malnutrition, has a life-extending effect in animals, and methionine (met) and cysteine (cys) have a special role. Diets restricted only in met extend lifespan, and animals on DR plus high levels of met and cys lose the benefits of DR. Life-extension via DR is due in part to hydrogen sulfide signaling. Cysteine is a source for hydrogen sulfide production, yet DR increases hydrogen sulfide production. Here we examine how DR affects organismal oxidation rates of ingested cysteine. Because excess cysteine is oxidized through a pathway that does not produce hydrogen sulfide, our hypothesis is that DR will decrease cysteine oxidation. We compare cysteine to equimolar alanine (ala), which is identical in structure save the hydrogen sulfide group. DR slightly increased oxidation of both cys and ala only at 24 h post-feeding, but not from 1–7 h. Moreover, ala consistently was oxidized ~5-fold more than cys (from 2–24 h). Hence, changes in cys oxidation in response to DR were minimal. Reduced reproduction also extends lifespan in many animals, but the mechanism is not known to involve cys. Consistent with this, life-extending ovariectomy (OVX) had no effect on cys oxidation (1–11 h). Ala oxidation was, again, ~5-fold greater than cys oxidation in controls (from 3–7 h). Surprising to us, ala oxidation was repressed upon OVX to the same low rate as cys oxidation. These results suggest that organismal oxidation rates of cys are not altered greatly upon DR or OVX, but that oxidation rates of cys may be low relative to other amino acids also oxidized via pyruvate.
