Biochimica et biophysica acta最新文献

The biosynthesis of phosphomannan by cultures of Hansenula holstii NRRL Y-2448 has been demonstrated to proceed from glucose with all carbons remaining intact. Enzymes were found in cell-free extracts capable of converting glucose to guanosine diphosphate mannose via mannose 1-phosphate. The isomerization of glucose to mannose occured as hexose phosphate and not as nucleotide hexose. The isolation and identification of guanosine diphosphate mannose from perchloric acid extracts gave further evidence for the proposal that guanosine diphosphate mannose is a precursor of phosphomannan.

Mitochondria isolated from cockroach thoracic muscles have been used to demonstrate that the rate of oxidation of several Krebs-cycle intermediates is under the control of adenosine diphosphate concentration. Respiratory-control indices as high as 25 have been achieved with both pyruvate and glutamate. Contrarily, the rate of oxidation of α-glycerol phosphate is influenced by adenosine diphosphate concentration to only a minor degree, but is markedly inhibited by accumulation of the oxidation product. When the ratio [reactant]/[product] is approx. 3, oxidation of α-glycerol phosphate becomes very low. These findings are used to propose a theory which may satisfactorily explain the problem of respiratory control in insect muscles.

A suspension of epithelial cells of the human tongue has been shown to form glycogen and CO₂ from glucose, fructose, maltose and sucrose. Carbon 1 of glucose is converted to CO₂ much more rapidly than carbon 6.

The properties of the glucose-transport system of Escherichia coli K10 were studied by following intracellular accumulation of ¹⁴C-labeled α-methylglucoside. A mutant defective in the uptake of glucose was found to be unable to accumulate α-methylglucoside to a significant level, confirming the view that the carrier for glucose also acts on α-methylglucoside. Although the glucoside was not incorporated into cellular constituents or metabolized for energy, about one-half of the accumulated molecules underwent phosphorylation while one-half remained as the free glucoside. Studies on the inhibition of uptake of the glucoside showed that the affinity of the compound depended upon the substituents on C-2, C-3 and C-6. Structural modifications at C-1, on the other hand, had relatively little effect on the affinity unless a large aglycone was added. α-Methylglucoside accumulated by the cells was gradually lost upon dilution of the cells in simple inorganic medium. The rate of exit could be accelerated by two groups of compounds: non-metabolizable structural analogs with affinity for the transport carrier and metabolizable compounds which entered the cell by other routes. The effect of the latter group depended upon their further metabolism within the cell rather than their own direct effects on the carrier system.

Rabbit serum globulins were complexed with bromoacetyl cellulose. Under appropriate conditions 96 to 98% of the protein was chemically bound. Binding of the globulins required a preliminary physical adsorption followed by a chemical reaction. The solid globulin-cellulose complex, under the conditions used, adsorbed specific antigens from solution completely, up to a maximum amount which represented a ratio of antibody to antigen close to that found in a specific precipitate in the equivalence zone. Preliminary experiments are reported on the problems of the specificity of adsorption of homologous antigen compared to unrelated proteins, and of the elution of adsorbed antigen. Potential uses for this method in biochemical investigations are suggested.