Given a passage with a context and an answer, construct a question on the basis of the information present in the passage. Construct the question in such a way that (i) it is unambiguous, (ii) it is answerable from the passage, (iii) its answer is unique (iv) it answer uses text phrases from the passage. Avoid creating questions that (i) can't be answered correctly without actually understanding the passage and (ii) uses the same words or phrases given in the passage.

[EX Q]: Context: Cysteine, a sulfur-containing amino acid, plays an important role in a variety of cellular functions such as protein biosynthesis, methylation, and polyamine and glutathione syntheses. In trypanosomatids, glutathione is conjugated with spermidine to form the specific antioxidant thiol trypanothione (T[SH]2) that plays a central role in maintaining intracellular redox homeostasis and providing defence against oxidative stress.', 'We cloned and characterised genes coding for a cystathionine β-synthase (CβS) and cysteine synthase (CS), key enzymes of the transsulfuration and assimilatory pathways, respectively, from the hemoflagellate protozoan parasite Trypanosoma rangeli.', 'Our results show that T. rangeli CβS (TrCβS), similar to its homologs in T. cruzi, contains the catalytic domain essential for enzymatic activity. Unlike the enzymes in bacteria, plants, and other parasites, T. rangeli CS lacks two of the four lysine residues (Lys26 and Lys184) required for activity. Enzymatic studies using T. rangeli extracts confirmed the absence of CS activity but confirmed the expression of an active CβS. Moreover, CβS biochemical assays revealed that the T. rangeli CβS enzyme also has serine sulfhydrylase activity.
Answer: These findings demonstrate that the RTS pathway is active in T. rangeli, suggesting that this may be the only pathway for cysteine biosynthesis in this parasite. In this sense, the RTS pathway appears to have an important functional role during the insect stage of the life cycle of this protozoan parasite.
[EX A]: Is transsulfuration an active pathway for cysteine biosynthesis in Trypanosoma rangeli?

[EX Q]: Context: Evidence of hyperplasia with atypia found both on random periareolar fine needle aspiration (RPFNA) and in nipple aspirate fluid (NAF) fluid are associated with an increased risk for breast cancer.', 'In this study, we report the correlation of NAF production with cytological assessment of ductal cells obtained by RPFNA.', '113 women at high risk for development of breast cancer attending the Breast Cancer Prevention Clinic at the University of Kansas Medical Center underwent a single NAF collection attempt and RPFNA.', 'NAF was successfully collected in 51% of women. There was no significant difference in age, 5-year Gail risk assessment, menopausal status, hormone use, family history of breast cancer, history of prior atypical hyperplasia/LCIS or history of contralateral DCIS/invasive breast cancer between women who produced NAF and those that did not. The only significant difference between the two groups was in history of prior lactation (p = 0.018). Twenty-seven of the 113 subjects were found to have hyperplasia with atypia by RPFNA was 31% in women who produced NAF versus 16% in those who did not (p = 0.07).
Answer: Although prevalence of RPFNA atypia was numerically higher in NAF producers than non-producers the difference did not reach statistical significance. Failure to produce NAF does not exclude the presence of hyperplasia with atypia by random periareolar fine needle aspiration.
[EX A]: Does failure of high risk women to produce nipple aspirate fluid exclude detection of cytologic atypia in random periareolar fine needle aspiration specimens?

[EX Q]: Context: Underlying left ventricular (LV) dysfunction contributes to poor survival after operation to correct ischemic mitral regurgitation (IMR). Many surgeons do not appreciate that a key component of the Bolling undersized mitral ring annuloplasty concept is to decrease LV wall stress by altering LV shape, but precise 3-dimensional (3-D) geometric data do not exist substantiating this effect. We tested the hypothesis that annular reduction decreases regional circumferential LV radius of curvature (ROC) in a model of acute IMR.', 'Eight adult sheep underwent insertion of an adjustable Paneth-type annuloplasty suture and radiopaque markers on the LV and mitral annulus. The animals were studied with biplane videofluoroscopy during baseline conditions, then before and after tightening the annuloplasty suture during proximal left circumflex occlusion. End-systolic circumferential regional LV ROC and mitral annular area were computed.', 'Acute IMR was eliminated (MR grade 2.1+/-0.4 to 0.4+/-0.4, mean+/-SD, P<0.05) by tightening the Paneth annuloplasty suture. Paneth suture tightening during circumflex occlusion also decreased end-systolic regional circumferential radii of curvature at the basal (anterior, 3.40+/-0.16 to 3.34+/-0.14 cm; posterior, 3.31+/-0.23 to 3.24+/-0.26 cm; P<0.05) and equatorial levels (anterior, 2.99+/-0.21 to 2.89+/-0.29 cm; posterior, 2.86+/-0.38 to 2.81+/-0.41 cm; P<0.05).
Answer: Acute proximal circumflex occlusion caused IMR and increased end-systolic LV radii of curvature in this experimental preparation. Annular reduction sufficient to abolish IMR also decreased end-systolic anterior and posterior LV ROC, which would be expected to reduce LV wall stress and oxygen consumption in these regions, both potentially beneficial effects. The long-term effects of undersized annuloplasty on LV remodeling and function, however, will require further study in chronic animal preparations or patients with chronic IMR.
[EX A]:
Does undersized mitral annuloplasty alter left ventricular shape during acute ischemic mitral regurgitation?