An improved glucoseoxidase--peroxidase-coupled assay for -fructofuranosidase activity

An improved glucoseoxidase-peroxidase-coupled assay for the determination of β-fructofuranosidase activity is described. The method makes use of the double effect of Tris (2-amino-2-hydroxymethylpropane-1,3-diol) as an inhibitor of both invertase and contaminating glucosidases. The method is very sensitive and is suitable for routine determinations. The total time needed for a single analysis is less than half an hour.     

Isolation of adenosine 5'-diphosphate-L-glycero-D-mannoheptose, the assumed substrate of heptose transferase(s), from Salmonella minnesota R595 and Shigella sonnei Re mutants

From heptose transferase-less Re mutants of Salmonella minnesota and Shigella sonnei, a mixture of nucleotide-linked heptoses was isolated. After paper chromatography in different solvent systems, ADP derivatives of D-glycero-D-mannoheptose and L-glycero-D-mannoheptose could be isolated in pure form. The structure of ADP-L-glycero-D-mannoheptose was verified by analytical methods and by transformation of ADP-D-glycero-D-mannoheptose with ADP-D-glycero-D-mannoheptose-6-epimerase.     

The effect of age on the antigen-presenting mechanism in limiting dilution precursor cell frequency analysis

We have utilized limiting dilution analysis (LDA)2 to compare the intrinsic precursor cytotoxic T lymphocyte (pCTL) frequency for influenza-plus-self in young and old C57BL/6 mice. Under conditions of excess interleukin 2 (IL-2) and antigen presenting cells (APC) derived from spleens of mice matched in age to those being tested, we found more than a twofold difference in pCTL frequency between young and old animals. However, there was no difference in pCTL frequency between the two age groups if antigen was presented to the old responder cells on spleen cells derived from young mice. The apparent decrease in pCTL frequency in old mice by standard LDA may in fact be due to a defect in the antigen processing and/or presentation mechanism of old spleen cells. We conclude that the age-associated defective CTL activity previously reported by us and by others may be due at least in part to a defect in the antigen presentation mechanism of aging mice.