Intrinsic factor, free of R proteins, can be prepared from mouse stomach and used in a ligand assay specific for "true" cobalamin

A ligand assay specific for cobalamin that uses mouse stomach as the source of intrinsic factor has been developed. When mouse stomach extract incubated with radiocobalamin is fractionated by gel chromatography, the radioactive complex elutes as a single peak with apparent molecular weight of 54,900. Formation of the complex is greater than 98% inhibited by human anti-intrinsic factor antibody. When the equivalent of 10,000 pg/ml of cobinamide is added to serum, the apparent cobalamin concentration detected averages 8.5 pg/ml. Correlation with the Lactobacillus leichmannii microbiologic assay results in the regression equation y = 0.97x + 20. In six patients who had megaloblastic anemia the serum cobalamin by the mouse intrinsic factor ligand assay ranged from 0 to 9 pg/ml. Because the primary source of intrinsic factor is free of R proteins, there is no need for extensive purification of the extract. The assay is sensitive, precise, and accurate, and no more difficult to perform than other conventional ligand assay procedures.

Inhibitors of protein synthesis V. Irreversible interaction of antibiotics with an initiation complex

The initiation complex (t-complex) formed in a cell-free system (E. coli) from Ac-Phe-tRNA, poly(U) and washed ribosomes in the presence of initiation factors (ribosomal wash) and GTP, contains the Ac-Phe-tRNA bound quantitatively in a puromycin-reactive state. The t-complex is irreversibly inactivated by spiramycin with respect to its reactivity toward puromycin. The inactivated t-complex retains all of the Ac-Phe-tRNA bound, but it does not react with puromycin (2 x10-minus-3M) within 32 min at 25 degrees. In the case of another inhibitor protein synthesis, sparsomycin, the permanently "modified" t-complex not only retains all the bound Ac-Phe-tRNA but it can still react with puromycin. In the continuous presence of sparsomycin (1 x 10-minus-7M) the bound Ac-Phe-tRNA reacts quantitatively at a rate which is one-tenth the rate at which the t-complex reacts with puromycin, at low (6.25 x 10-minus-5M) or high (2 x 10-minus-3M) concentrations. These results are not in agreement with current views according to which aparsomycin binds to the ribosome reversibly at a single site with a KI in the range of 10-minus6-10-minus-7 M and according to which this stie is at the A'-site (puromycin site) of peptidyl transferase.

Infrared and Raman spectra of the cerium(IV) ion – nitrate ion – water system

Infrared spectra of aqueous solutions containing Ce(IV) and nitrate ions have been obtained by the attenuated total reflectance (a.t.r.) technique. Vibration frequencies and intensities have been measured and compared with infrared transmittance spectra and Raman spectra of both solutions and solids. The number of bands and the variation of band intensity with concentration changes indicate the presence of nitrato–cerium complexes in the solution. The polarization of the 1 538 cm−1 Raman band is advanced as a criterion that the coordination between the nitrate ion and the cerium(IV) ion is bidentate. Possible assignments are considered although many of the vibrations are characteristic of the ligand and hence are not diagnostic of a particular species.