THREONINE AND METHIONINE ARE LIMITING AMINO-ACIDS FOR PROTEIN-SYNTHESIS IN PATIENTS WITH AIDS

This study was conducted to identify the most rate-limiting amino acid s for whole-body protein synthesis in acquired immunodeficiency syndro me (AIDS) patients. We postulated that an essential amino acid that wo uld be rate limiting in AIDS should have a low basal plasma concentrat ion and should remain at a low level during amino acid infusion. Seven male AIDS patients (median age 37 y, CD4 cell count: 76 mm(-3)) witho ut any clinically active opportunistic infection during the month befo re the experiment were infused intravenously with a complete amino aci d-glucose mixture for 2.5 h. Eight healthy volunteers were used as con trols. Before the infusion, the concentrations of most free essential amino acids (methionine, threonine, histidine, isoleucine, leucine and tryptophan) were significantly lower (P < 0.05) in AIDS patients than in controls. Most plasma free essential amino acids increased signifi cantly during infusion. However, the absolute increase above basal lev els for threonine, valine, lysine, (P < 0.05) and methionine (P < 0.07 3) was smaller in AIDS patients than in control subjects. Thus, threon ine and possibly methionine may be rate limiting for whole-body protei n synthesis in AIDS patients, suggesting that there are selective amin o acid requirements in patients with AIDS.