Studies on the subsite structure of amylases. I. Interaction of glucoamylase with substrate and analogues studied by difference-spectrophotometry

Studies were made on the ultraviolet difference-spectra of glucoamylase from Rhizopus niveus [EC 3.2.1.3] specifically produced by the substrate maltose and the inhibitors, glucose, glucono-1: 5-lactone (gluconolactone), methyl beta-D-glucoside, cellubiose, and cyclohexa-, and cyclohepta-amyloses. Of these, maltose and gluconolactone produced characteristic difference spectra with a trough near 300 nm. Based on studies with a model compound for a tryptophan residue, Ac-Trp, this trough was attributed to the effect of a negative charge upon the tryptophan residue. From the concentration dependency of the difference spectra, the dissociation constants of the complexes between the enzyme and maltose, glucose, and gluconolactone were evaluated to be 1.2 mM, 51 mM, and 1.5 mM, respectively. These values are in good agreement with the values of Km or K1 obtained from the steady-state kinetics. The difference-spectrophotometric data suggested that referring to the values of subsite affinities of glucoamylase, maltose, and gluconolactone occupy mainly Subsite 1, where the non-reducing-end glucose residue of a substrate is bound in a productive form and that a tryptophan residue with shows a trough near 300 nm in difference spectra is located in this subsite.

Post-exposure prophylaxis of murine rabies with polyinosinic-polycytidylic acid and chlorite-oxidized amylose

Chlorite-oxidized amylose (COAM), polyinosinic-polycytidylic acid [poly(I:C)], and combinations of the two drugs were evaluated for their interferon-inducing properties and their ability to protect mice against rabies infection. Post-exposure administration of one or two doses (100 mug each) of poly(I:C) significantly protected mice against rabies infection. Pretreatment of mice with COAM 3 h before poly(I:C) stimulation resulted in an enhancement of the interferon response. However, the increased interferon titers were not reflected by increased protection against rabies infection over that achieved with poly(I:C) therapy alone. Therapy with COAM alone did not protect mice against rabies but, rather, was associated with enhanced mortality.

Polyacetal carboxylic acids: a new group of antiviral polyanions

Chlorite-oxidized oxypolysaccharides are polyacetal carboxylic acids. They inhibited the cytopathic effect of vesicular stomatitis virus in mouse embryo cell cultures challenged at low input multiplicity. After intraperitoneal injection of these compounds in mice, interferon appeared in the circulation. The compounds also protected mice against lethal mengovirus infection and against the development of experimental pox lesions on the tail. Chlorite-oxidized oxyamylose was antiviral only when at least 64% of the glucopyranose units were oxidized, an observation which suggested a correlation between charge density and antiviral effect. The antiviral activity was also influenced by the molecular weight, as demonstrated by the fact that chlorite-oxidized dextrans which had a high intrinsic viscosity were more active than those with low intrinsic viscosity.