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The γ-ray spectra arising from the decay of 41-day 148Pmm and 5-day 148Pmg produced by the irradiation of 2.6-year 147Pm in a thermal reactor neutron flux have been measured with a Ge(Li) detector. The absolute probabilities for γ-ray emission were determined from an analysis of the spectra and used to construct an improved decay scheme for the two isomers and to obtain their production cross sections. The 147Pm thermal neutron cross sections obtained after making a small correction for epithermal capture are 84 ± 10 b and 72.4 ± 3.0 b for the production of the 148Pmg and 148Pmm activities respectively, in good agreement with the results of Fenner and Large, but significantly smaller than other recent measurements.

Summary Previous work has shown that cytochrome c -552 from Chromatium contains a covalently bound flavin, which is not released by denaturation but is liberated by proteolysis or various chemical treatments and that the protein is probably attached at the 8α position of the FAD. In the present study unambiguous evidence was obtained for 8α substitution from (a) ESR hyperfine spectra of the flavin cation radical and (b) from identification of the flavin released by performic acid oxidation from cytochrome c -552 as riboflavin-8α-carboxylic acid. Various lines of evidence suggest that in the native enzyme a reduced sulfur may be linked to the 8α group of the flavin, similarly to monoamine oxidase, which contains cysteinyl 8α-FAD, although the conditions required for cleavage of the flavin from the two enzymes appear to be quite different.

The amino acid sequence of the coenzyme binding site of beef heart succinate dehydrogenase is serine-histidine-threonine-valine-alanine. Flavin adenine dinucleotide is covalently bound to a ring nitrogen of histidine through the 8α position of the isoalloxazine ring system.

Fission yields of 135I and 140Ba have been measured relative to the yields from 235U for samples of different fissile materials irradiated in the NRU reactor in a flux of 2.7 × 1014 neutrons/cm2 sec for 24 hours. The relative 135I contents of the samples were determined from the reactivity effect of the daughter 135Xe in the Chalk River Pool Test Reactor using a pile oscillator. The relative concentrations of 140Ba were determined by gamma-ray counting of the daughter 140La. The fractional yields, normalized to 0.0625 for both fission products in 235U fission, are:[Formula: see text]In the fission of 233U and 239Pu the cumulative yields to 135I and 140Ba are approximately 20% and 7% less than the mass-spectrometrically-measured cumulative yields to 135Cs and 140Ce respectively. The differences are attributed to direct formation of 135Xe and 140La.

Previously described methods for identification of proteins separated in cylindrical polyacrylamide gels have been found to be costly in time and antiserum and difficult to apply to small amounts of protein as are found in cerebrospinal fluid. We describe a method which involves printing of the proteins on the cut surface of the gel onto nitrocellulose paper. The protein bands of the imprint can then be identified using labelled antibodies. We have found this to be economical and quick, and it has permitted sensitive and reliable identification of proteins in unconcentrated cerebrospinal fluid and aqueous humour.

Publisher Summary This chapter focuses on covalently bound flavin active center of succinate dehydrogenase. It has been known since the early 1950s that membrane fragments of heart mitochondria contain a form of flavin which is not released by denaturation but is extracted in soluble form only after extensive proteolysis. Kearney isolated the first pure flavin peptide from a proteolytic digest of highly purified succinate dehydrogenase by a series of ion exchange chromatographic procedures. The flavin peptide and its acid hydrolysis product differed from free flavins in three important respects: they were much more water soluble, they showed a considerable hypsochromic shift of the absorption spectrum in the neutral, oxidized form, with the 375-mμ band shifted to 345–350 mμ, and they showed a characteristic pH fluorescence curve, not seen with free flavins.

Previous studies in this laboratory have shown that the active center of hepatic monoamine oxidase contains flavin dinucleotide covalently linked to the peptide chain via the 8α position of the flavin but that, unlike in succinate dehydrogenase, the linkage is not to histidine but to another amino acid. A pure flavin pentapeptide has now been isolated from monoamine oxidase which yields on acid hydrolysis or digestion with aminopeptidase M 1 mole each of serine and tyrosine and 2 of glycine and gives a positive test for sulfur. Oxidation of the peptide with performic acid yields, in addition to the amino acids mentioned, cysteic acid. The physical and chemical properties of the peptide are in accord with the conclusion that the amino acid substituted on the 8α group of the flavin is cysteine in thioether linkage. Edman degradation followed by dansylation revealed the sequence

Flavin peptides derived from monoamine oxidase, free from succinate dehydrogenase flavin, were obtained by digestion of outer membranes of beef liver mitochondria with trypsin and chymotrypsin and purification by various chromatographic methods. The flavin peptides show the same hypsochromic shift of the optical absorption spectrum as flavin peptides from succinate dehydrogenase: the 370 mμ band of the neutral oxidized flavin is shifted to 340 mμ, whereas the cation shows a peak at 370 mμ. The ESR spectrum of the monoamine oxidase flavin cation radical also resembles that of succinate dehydrogenase flavin in that the total width is reduced from 49 G (in riboflavin) to at least 45 G, and the line width from 3.8 G (in riboflavin) to 2.3 G. The covalently bound flavins of monoamine oxidase and succinate dehydrogenase differ, however, in that the former shows the same fluorescence intensity between pH 3.4 and 8, while the latter is quenched with a pK of 4.5 ± 0.1. These observations indicate that the FAD of monoamine oxidase is covalently linked to the peptide chain through the 8α-CH 3 group of riboflavin but histidine is not the immediate substituent, as in succinate dehydrogenase. Hydrolysis of flavin peptides from monoamine oxidase in 6 N HCl at 95° yields a derivative chromatographically distinct from free flavins which is ninhydrin-positive and thus contains an amino acid bound to the 8α-position.

Lumiflavin was synthesized, containing 52% isotope 13 C substituted in position 12, and the corresponding cation, neutral and anion free radicals were prepared. From the ESR spectra of these radicals the spectra correponding to 100% 13 C substitution were calculated. The value of the isotropic coupling constant for both N-5 and C-12 was determined from these spectra and their signs are discussed. With careful choice of σ-π spin polarization parameters, we found that both the anion and cation radicals have almost 50% of the total spin density located on the adjacent N-5 and C-12 stoms. These results are discussed in terms of chemical and biochemical reactivity.

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Acid hydrolysis of flavin peptides from the active center of mammalian succinate dehydrogenase yields a substituted riboflavin which was isolated in pure form. It contains a substituent attached to position 8α of riboflavin. Drastic acid hydrolysis of this compound and catalytic hydrogenation yield nearly 1 mole of free histidine. Histidine is also liberated on neutral photolysis. The presence of histidine is confirmed by behavior on high voltage electrophoresis at various pH values and by acid titration curves. Linkage of the 8α-CH3 group of riboflavin is to one of the imidazole ring nitrogens since neither the flavin peptide nor its acid derivative give a Pauly reaction. This assignment is in full accord with the characteristic pH-fluorescence curve of covalently bound flavin. The pK of the fluorescence quenching agrees with that expected for the imidazole nitrogen in histidyl flavin.