Effect of hyper-osmotic stress on alanine content of Leishmania major promastigotes.
Earlier studies showed that Leishmania major promastigotes are sensitive to osmotic conditions. A reduction in osmolality caused the cells to shorten and to rapidly release most of their large internal pool of alanine. In this study some effects of hyper-osmotic stress were examined. An increase in osmolality of the culture medium from 308 to 625 mOsm/kg caused only a small decrease in growth rate. When cells grown in the usual culture medium (308 mOsm/kg) were washed, resuspended in iso-osmotic buffer, and subjected to acute hyper-osmotic stress by addition of mannitol, the alanine content increased even in the absence of exogenous substrate. Promastigotes, depleted of alanine by a 5-min exposure to hypo-osmotic conditions, also synthesized alanine when resuspended in iso-osmotic buffer. Washed cells resuspended in iso-osmotic buffer consume their internal pool of alanine under aerobic conditions. Rates of consumption decreased on addition of mannitol, becoming zero at about 440 mOsm/kg. At higher osmolalities, alanine synthesis occurred. To estimate whether proteolysis could account for alanine synthesis in the absence of exogenous substrate, cells that had been grown with [1-14C]leucine were washed and resuspended under hypo-, iso-, and hyper-osmotic conditions and the amounts of 14CO2 and 14C-labelled peptides released in 1 h were measured. Little proteolysis occurred under these conditions, but the possibility that proteolysis was the source of the alanine increase, observed in response to hyper-osmotic stress, cannot be ruled out.
Burrows
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Department of Cell Biology, Duke University Medical Center, Durham, North Carolina 27710.
Blum
J J
JJ
D000409:Alanine / Q000378:metabolism*; D000818:Animals; D005947:Glucose / Q000378:metabolism; D007895:Leishmania tropica / Q000254:growth & development / Q000378:metabolism*; D009994:Osmolar Concentration; D010447:Peptide Hydrolases / Q000378:metabolism
D010447:Peptide Hydrolases; D005947:Glucose; D000409:Alanine