SummaryThe partial alpha emitting lanthanide isotopeThe excitation functions for light- and heavy ion induced reactions have been calculated using the ALICE91 code. The direct nuclear reactionThe lower cross section of the spallation process can be compensated by using very thick targets. On-line mass separation technique provides high purity isotopically clean

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Crystalline preparations of human parotid amylase were separated by recycling chromatography into two families of isoenzymes : family A, comprising isoenzymes 5, 3, and 1 and family B, comprising isoenzymes 4 and 2. The isoenzymes of family A are glycoenzymes whereas those of family B are not. The carbohydrate moiety of family A contains 6 moles of glucosamine, 3 moles of fucose, 2 moles of mannose, and 2 moles of galactose per mole of glycoenzyme. No sialic acid was detected. The neutral sugars were qualitatively and quantitatively the same in amylases isolated from three individuals. The isoenzymes of both families appear to be single polypeptide chains with molecular weights of 62,000 for the glycosidated proteins of family A and 56,000 for the nonglycosidated protein of family B. N o amino-terminal group Materials Ovalbumin, bovine serum albumin, sodium dodecyl sulfate, NADP+, DTNB,' and Triton X-100 were obtained from

Mutants with enhanced P-lactam resistance were selected from strains of Enterobacter cloacae and E. aerogenes by using three antibiotics. High-level ,Blactamase-producing mutants had similar degrees of increased resistance, enzyme substrate profiles, and isoelectric (pl) values irrespective of the selective agent. Reverse mutants from a resistant E. cloacae mutant regained the susceptibility pattern originally exhibited by the wild type, or were of enhanced susceptibility, and no longer expressed increased P-lactamase production. ,-Lactamases of the mutants were similar in pI values to the wild-type enzyme. The increased resistance of the mutants therefore appeared to be accounted for by increased Plactamase production.Previous studies from this laboratory (4, 10) and others (18) have shown that cefamandoleand ampicillin-resistant mutants of Enterobacter species occur at a frequency as great as 10-5.Two classes of resistant mutants were selected by the antibiotics, one of which had markedly enhanced ability to inactivate the antibiotic in vitro. In our studies, the proportions of these two classes of mutants were approximately equal. We suggested that cefamandole resistance of the mutants with increased ,-lactamase production might be explained by a mutational change involving the enzyme which extended its spectrum of activity to include cefamandole. We further demonstrated cross-resistance between ampicillin and cefamandole in strains with enhanced enzyme production. Ott et al. (18) reported a lack of correlation between 3-lactamase production and susceptibility to cefamandole, found no qualitative differences between the substrate specificities of enzymes from a wildtype Enterobacter strain and its enhanced enzyme-producing mutant, and concluded that these mutants may have owed their resistance to genetic determinants other than those coding for ,-lactamase production.This study focused exclusively on mutants with enhanced 1-lactamase production and was designed to resolve these differences in interpretation.

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