L-canavanine inhibits L-arginine uptake by broiler chicken intestinal brush border membrane vesicles.

1. Intestinal brush border membrane vesicles (BBMV) were prepared from 3-week-old broiler chickens. 2. Electron microscopy of the BBMV fraction showed single membrane vesicles of different sizes with no electron dense material inside. No other organelles were observed. The sucrase and maltase activities were enriched by factors of 16 and 18, respectively, in the BBMV fraction in comparison with the homogenate. On the other hand, the Na+/K+-ATPase sensitivity to ouabain was increased by a factor of 0.8. 3. The BBMV showed a maximum L-[14C]-arginine uptake (944.9 +/- 22.9 pmoles/mg protein) at 45 s and thereafter it declined slowly. In the presence of 0.5 mM L-canavanine, the L-[14C]-arginine uptake by BBMV was reduced by 43.6% at 45 s. 4. It is concluded that L-canavanine inhibits L-arginine Na+-dependent transport across the enterocyte apical membrane in a highly purified intestinal BBMV from broiler chickens.

Screening of substrate analogs as potential enzyme inhibitors for the arginine kinase of Trypanosoma cruzi.

Arginine kinase catalyzes the transphosphorylation between phosphoarginine and ADP. Phosphoarginine is involved in temporal ATP buffering and inorganic phosphate regulation. Trypanosoma cruzi arginine kinase phosphorylates only L-arginine (specific activity 398.9 x mUE-min(-1) x mg(-1)), and is inhibited by the arginine analogs, agmatine, canavanine, nitroarginine, and homoarginine. Canavanine and homoarginine also produce a significant inhibition of the epimastigote culture growth (79.7% and 55.8%, respectively). Inhibition constants were calculated for canavanine and homoarginine (7.55 and 6.02 mM, respectively). In addition, two novel guanidino kinase activities were detected in the epimastigote soluble extract. The development of the arginine kinase inhibitors of T. cruzi could be an important feature because the phosphagens biosynthetic pathway in trypanosomatids is different from the one in their mammalian hosts.

Human purified alpha-fetoprotein: I. In vitro effects on lymphocyte proliferation to mitogens and on mixed lymphocyte reactivity

Estudou-se o efeito de alfafetoproteína (AFP) sobre a proliferaçäo de linfócitos periféricos humanos estimulados por fitohemaglutinina (PHA), concanavalina A (Con A), pokeweed mitogênio (PWM) e por células alogênicas em culturas mistas de linfócitos, ao medir-se e comparar-se a incorporaçäo de timidina triciada (parâmetros de crescimento celular) em culturas contendo AFP humanas purificada e em culturas sem a proteína (controles). Nenhuma alteraçäo quantitativa na reatividade linfocitária foi verificada nas culturas com AFP