In this work, pure MCM-41 mesoporous silica with active mesoporous sites has been successfully applied, as a highly efficient and recoverable catalyst, for the rapid and convenient synthesis of α-aminonitriles and imines. Various imines, as the intermediate of the Strecker reaction, were simply prepared from condensation of a wide range of aldehydes and amines in the presence of low loading of MCM-41 mesoporous silica under solvent-free conditions at room temperature in high to quantitative yields. Furthermore, the corresponding α-aminonitrile derivatives were prepared through the three-component Strecker reaction using trimethylsilylcyanide catalyzed by MCM-41 as a bifunctional heterogeneous mesoporous solid catalyst.

CPT (carnitine palmitoyltransferase) II muscle deficiency is the most common form of muscle fatty acid metabolism disorders. In contrast to carnitine deficiency, it is clinically characterized by attacks of myalgia and rhabdomyolysis without persistent muscle weakness and lipid accumulation in muscle fibers. The biochemical consequences of the disease-causing mutations are still discussed controversially. CPT activity in muscles of patients with CPT II deficiency ranged from not detectable to reduced to normal. Based on the observation that in patients, total CPT is completely inhibited by malony-CoA, a deficiency of malonyl-CoA-insensitive CPT II has been suggested. In contrast, it has also been shown that in muscle CPT II deficiency, CPT II protein is present in normal concentrations with normal enzymatic activity. However, CPT II in patients is abnormally sensitive to inhibition by malonyl-CoA, Triton X-100 and fatty acid metabolites. A recent study on human recombinant CPT II enzymes (His 6 -N-hCPT2 and His 6 -N-hCPT2/S113L) revealed that the wild-type and the S113L variants showed the same enzymatic activity. However, the mutated enzyme showed an abnormal thermal destabilization at 40 and 45 • C and an abnormal sensitivity to inhibition by malony-CoA. The thermolability of the mutant enzyme might explain why symptoms in muscle CPT II deficiency mainly occur during prolonged exercise, infections and exposure to cold. In addition, the abnormally regulated enzyme might be mostly inhibited when the fatty acid metabolism is stressed.

Objective:Muscle carnitine palmitoyltransferase (CPT) II deficiency, the most common defect of lipid metabolism in muscle, is characterized by attacks of myoglobinuria without persistent muscle weakness.Methods:His6-N-hCPT2 (wild-type) and His6-N-hCPT2/S113L (variant) were produced recombinantly in prokaryotic host and characterized according to their functional and regulatory properties.Results:The wild-type and the variant S113L showed the same enzymatic activity and thermostability at 30°C. The mutated enzyme, however, revealed an abnormal thermal destabilization at 40°C and 45°C. This was consistent with an increased flexibility (B-factor) of the variant at 40°C compared with that of the wild-type shown by molecular dynamics analysis. Preincubation of the enzymes with l-carnitine and acyl-l-carnitines containing more than 10 carbons in the acyl side-chain stabilized the mutated enzyme against thermal inactivation. In contrast, palmitoyl-CoA destabilized both enzymes.Conclusions:The problems in CPT II deficiency originating from the S113L mutation are not caused by the loss of catalytically active enzyme. They might be at least partially related to an impaired thermal stability of the protein. The lower thermodynamic stability of the variant might explain why fever and prolonged exertion provoke attacks of myoglobinuria in CPT II deficiency. The stabilization by acyl-l-carnitines might provide the basis for possible preventive therapy of CPT II deficiency.

No abstract

No abstract