Subject(s)
Amines/toxicity , Consumer Product Safety , Food Handling , Salmonella typhimurium/genetics , Amines/administration & dosage , Amines/chemistry , Amines/metabolism , Amines/pharmacokinetics , Animals , Carcinogenicity Tests , Humans , Mutagenicity Tests , Rats , Risk Factors , Salmonella typhimurium/drug effectsABSTRACT
An unusual presentation of Leigh's disease consisting of rapid progression of leg weakness in a young child is discussed. Magnetic resonance imaging revealed an intramedullary mass lesion of the conus medullaris. Surgical exploration revealed only necrosis and inflammation. Subsequent studies revealed pathology in the cerebrum as well as the spinal cord. Metabolic abnormalities confirmed the diagnosis of Leigh's disease. The differential diagnosis of intramedullary mass lesions demonstrated by magnetic resonance imaging should include metabolic, inflammatory, and ischemic processes as well as neoplastic disease.
Subject(s)
Leigh Disease/diagnosis , Spinal Cord Neoplasms/diagnosis , Adult , Diagnosis, Differential , Humans , Leigh Disease/diagnostic imaging , Leigh Disease/surgery , Magnetic Resonance Imaging , Male , Tomography, X-Ray Computed , UltrasonographyABSTRACT
Differential scanning calorimetry has been used to investigate the thermodynamics of denaturation of ribonuclease T1 as a function of pH over the pH range 2-10, and as a function of NaCl and MgCl2 concentration. At pH 7 in 30 mM PIPES buffer, the thermodynamic parameters are as follows: melting temperature, T1/2 = 48.9 +/- 0.1 degrees C; enthalpy change, delta H = 95.5 +/- 0.9 kcal mol-1; heat capacity change, delta Cp = 1.59 kcal mol-1 K-1; free energy change at 25 degrees C, delta G degrees (25 degrees C) = 5.6 kcal mol-1. Both T1/2 = 56.5 degrees C and delta H = 106.1 kcal mol-1 are maximal near pH 5. The conformational stability of ribonuclease T1 is increased by 3.0 kcal/mol in the presence of 0.6 M NaCl or 0.3 M MgCl2. This stabilization results mainly from the preferential binding of cations to the folded conformation of the protein. The estimates of the conformational stability of ribonuclease T1 from differential scanning calorimetry are shown to be in remarkably good agreement with estimates derived from an analysis of urea denaturation curves.
Subject(s)
Ribonuclease T1/chemistry , Thermodynamics , Calorimetry, Differential Scanning , Enzyme Stability , Hydrogen-Ion Concentration , Protein Conformation , Protein Denaturation , Spectrometry, FluorescenceABSTRACT
To investigate the pH dependence of the conformational stability of barnase, urea denaturation curves were determined over the pH range 2-10. The maximum conformational stability of barnase is 9 kcal mol-1 and occurs between pH 5 and 6. The dependence of delta G on urea concentration increases from 1850 cal mol-1 M-1 at high pH to about 3000 cal mol-1 M-1 near pH 3. This suggests that the unfolded conformations of barnase become more accessible to urea as the net charge on the molecule increases. Previous studies suggested that in 8 M urea barnase unfolds more completely than ribonuclease T1, even with the disulfide bonds broken [Pace, C.N., Laurents, D. V., & Thomson, J.A. (1990) Biochemistry 29, 2564-2572]. In support of this, solvent perturbation difference spectroscopy showed that in 8 M urea the Trp and Tyr residues in barnase are more accessible to perturbation by dimethyl sulfoxide than in ribonuclease T1 with the disulfide bonds broken.
