Conformational changes are crucial for the catalytic action of many enzymes. A prototypical and well-studied example is loop opening and closure in triosephosphate isomerase (TIM), which is thought to determine the rate of catalytic turnover in many circumstances. Specifically, TIM loop 6 \"grips\" the phosphodianion of the substrate and, together with a change in loop 7, sets up the TIM active site for efficient catalysis. Crystal structures of TIM typically show an open or a closed conformation of loop 6, with the tip of the loop moving ∼7 Å between conformations. Many studies have interpreted this motion as a two-state, rigid-body transition. Here, we use extensive molecular dynamics simulations, with both conventional and enhanced sampling techniques, to analyze loop motion in apo and substrate-bound TIM in detail, using five crystal structures of the dimeric TIM from Saccharomyces cerevisiae. We find that loop 6 is highly flexible and samples multiple conformational states. Empirical valence bond simulations of the first reaction step show that slight displacements away from the fully closed-loop conformation can be sufficient to abolish most of the catalytic activity; full closure is required for efficient reaction. The conformational change of the loops in TIM is thus not a simple \"open and shut\" case and is crucial for its catalytic action. Our detailed analysis of loop motion in a highly efficient enzyme highlights the complexity of loop conformational changes and their role in biological catalysis.

Reverse Phase Protein Arrays (RPPA) were applied for the quantification and validation of protein biomarkers of beef qualities on M. longissimus thoracis sampled early post-mortem from young Charolais bulls. pHu was related to six proteins, three of which are glycolytic enzymes (ENO1, ENO3 and TPI1), while others belong to structural (TTN and α-actin) and proteolytic (μ-calpain) pathways. For color traits, several correlations were found, interestingly with structural proteins. The relationships were in some cases trait-dependent. To understand the mechanisms and explore animal variability, color data were categorized into three classes. α-actin and TTN allowed efficient separation of the classes and were strongly related with all color traits. Biomarkers belonging to heat stress and metabolism pathways were also involved. Two identified proteins, namely Four and a half LIM domains 1 (FHL1) and Tripartite motif-containing 72 (TRIM72), were for the first time related to beef color. Overall, these relationships could be used to develop muscle-specific processing strategies to improve beef color stability.

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A 15-month-old girl with severe hemolytic anemia and progressive respiratory failure is presented. She was well until the age of six months when she developed a pulmonary infection. During the next six months, she had frequent respiratory infections and her paleness became evident. At the age of 12 months, she was observed to have easy fatigability and muscle weakness, and she received her first blood transfusion. She was referred to our hospital at the age of 15 months. The physical examination revealed a malnourished girl with hypotonia, nystagmus, generalized muscle weakness and severe breathing difficulty requiring ventilatory support The hemoglobin (Hb) was 9.7 g/dl; hematocrit (Hct) 29%, mean corpuscular volume (MCV) 101 fl and reticulocyte count 15%. Peripheral blood smear revealed macrocytosis and stomatocytosis (30% of the red cells) and polychromasia. Sweat chloride test was 90 and 94 mEq/L on two separate occasions. The serum vitamin E level was 0.26 mg/dl (N: 0.44-0.68). She was found to be heterozygous for factor V Leiden mutation. Although malnutrition, low serum vitamin E and elevated sweat chloride test were suggestive of cystic fibrosis, this diagnosis failed to account for all the findings in the patient. A search for a red cell enzyme deficiency revealed that the red cell triosephosphate isomerase (TPI) activity was low. DNA analysis showed the 315 G-C (105 Glu-Asp) TPI mutation, thus confirming the diagnosis of TPI deficiency.

A 12-year-old girl had chronic nonspherocytic hemolytic anemia due to triosephosphate isomerase deficiency. Developmental and motor delay and muscular weakness were followed by cerebellar dysfunction and finally spasticity with hyperreflexia. Abnormal histopathological findings were hyaline cell bodies and axonal \"spheroids\" in the hypothalamus and cerebellar cortex, severe neuronal loss in the dentate and olivary nuclei, and partial loss of cerebellar Purkinje\'s and granular layer cells (olivocerebellar atrophy).

Prenatal diagnosis: The authors present a personal case of triose-phosphate-isomerase deficiency. Clinically the deficiency associates a constitutional non spherocytic anemia, paroxystic and precocius, and neuromuscular symptoms (axial hypotonia and limb palsies). A diaphragmatic paralysis may complicate the syndrome. Infections are frequent. Survival rarely goes beyond 5 years of age. Biochemical exams show the ubiquity of the deficiency. The physiopathology remains obscure. The TPI deficiency is heritable (autosomal recessive transmission). The gene has been mapped on the short arm of the chromosome 12. Prenatal diagnosis is possible.

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A 16-month-old girl of Spanish origin with chronic hemolytic anemia and severe neuromuscular disease was found to have markedly reduced triosephosphate isomerase (TPI) activity in her erythrocytes, leukocytes, and plateletes. Both parents and some other family members had moderately reduced erythrocyte TPI activity in accordance with the autosomal recessive mode of inheritance in this enzymopathy. Latex ingestion and latex-stimulated histochemical NBT reduction by the patient\'s granulocytes were normal. Zymosan-stimulated superoxide radical (O-.2) formation, not previously studied in TPI-deficient granulocytes, was also within normal limits. Starchgel electrophoresis of TPI in both erythrocytes and leukocytes of the proposita and her parents was normal. Molecular studies of deficient TPI showed a normal kinetic pattern with markedly reduced heat instability. Immunologic studies demonstrated no cross reacting material in proposita leukocytes and a normal molecular specific activity. These studies suggest that molecular instability might cause both enzymatic and antigenic degradation of the TPI molecule and, therefore, TPI deficiency in our patient.