Analysis of Two Aspergillus nidulans Genes Encoding Extracellular Proteases

vanKuyk, P. A., Cheetham, B. F., and Katz, M. E. 2000. Analysis of two Aspergillus nidulans genes encoding extracellular proteases. Characterization of prtAΔ mutants, generated by gene disruption, showed that the prtA gene is responsible for the majority of extracellular protease activity secreted by Aspergillus nidulans at both neutral and acid pH. The prtAΔ mutation was used to map the prtA gene to chromosome V. Though aspartic protease activity has never been reported in A. nidulans and the prtAΔ mutants appear to lack detectable acid protease activity, a gene (prtB) encoding a putative aspartic protease was isolated from this species. Comparison of the deduced amino acid sequence of PrtB to the sequence of other aspergillopepsins suggests that the putative prtB gene product contains an eight-amino-acid deletion prior to the second active site Asp residue of the protease. RT-PCR experiments showed that the prtB gene is expressed, albeit at a low level.     

Structure of the linear, low molecular weight dextran synthesized by a d-glucosyltransferase (GTF-S3) of Streptococcus sobrinus

Four extracellular α-d-glucosyltransferases (GTF) have been separated from cultures of Streptococcus sobrinus strains grown in continuous culture. Three of the GTF synthesized soluble dextrans from sucrose, and one of these enzymes, GTF-S3, catalysed the production of a low molecular weight, linear dextran. Methylation analysis and high field proton NMR spectroscopy on the intact S3 glucans confirmed that these dextrans were small (dp 20–30) and linear, with the majority of chains terminated with a sucrosyl moiety. Enzymic hydrolysis, followed by analytical and semi-preparative HPLC, led to the isolation of only linear oligosaccharides, one of which was identified as 6^G-glucosylsucrose.The results are accommodated by the two-site insertion mechanism for dextran synthesis proposed by Robyt et al. (1974) (Arch. Biochem. Biophys., 165, 634).     

Removal of triton X-100 from aqueous solution using amberlite XAD-2.

Amberlite XAD-2 beads adsorb the nonionic detergent Triton X-100 over a wide range of conditions with a maximum capacity of 0.475 mmol/g dry weight. After treatment of protein solutions containing Triton X-100 with XAD-2 no interference by Triton with Folin assays was observed. Adsorption of Triton X-100 was favored by a free-energy change of ?835 cal/mol and by a positive entropy value. Adsorbed Triton could be completely desorbed and the XAD-2 regenerated with little loss in capacity by washing with propan-2-ol. Removal of Triton by XAD-2 was also successful in columns or bateh-wise on a pilot-plant scale.