Purification and characterization of α-glucosidases produced by Saccharomyces in response to three distinct maltose genes

α-Glucosidases or maltases (EC 3.2.1.20) were purified to electrophoretic homogeneity from a respective strain of Sacchromyces cerevisiae which carries a single MAL gene, either MALα, MALβ or MALγ, using gluconate-Sepharose affinity chromography and isoelectrofocusing. Of these maltases, two types of maltase were obtained from the MALγ strain, the pI values of which were 5.6 and 5.9. From the MALα and MALβ strain was obtained only one type of maltase with the pI at 5.6 which was identical to one of the maltases from the MALγ strain. These four maltases possessed the same properties, except for pI. They were monomers with molecular weights of between 66 000 and 67 000. With regard to the substrate specificity, they hydrolyzed maltose and sucrose exclusively but not α-methulglucoside nor maltooligosaccharide. They did not differ in immunological properties.     

DNA strand breaks in mammalian tissues induced by methylarsenics

DNA damage induced by administration of dimethylarsinic acid (DMAA) to rats and mice was investigated. At 12 h after administration of DMAA, DNA single-strand breaks were induced markedly in lung. The majority of dimethylarsine, one of the main metabolites, in the expired air was excreted within 6–18 h after administration of DMAA to rats. In vitro experiments using nuclei isolated from lung of mice indicated that DNA strand breaks were caused by dimethylarsine. Furthermore, the strand breaks after exposure to dimethylarsine were reduced in the presence of catalase and/or superoxide dismutase. These results strongly suggest that the strand breaks are induced not by dimethylarsine itself but by active oxygen, e.g., O ₂ ^? and ·OH, produced both by dimethylarsine and molecular oxygen. When DNA was exposed to dimethylarsine, thiobarbituric acid (TBA)-reactive intermediates andcis-thymine glycol were produced. Dimethylarsine appears to induce DNA damage by the mechanism similar to the damage produced by ionizing radiation.     

Serum-induced inhibition of isotonic fluid absorption by the kidney proximal tubule I. Mechanism of inhibition

Isotonic reabsorption by the rat kidney proximal tubule was drastically inhibited after less than 2 min intraluminal perfusion with fresh sera from rat (both homologous and autologous), cat, rabbit and human, but not with sera from mouse and guinea pig. The inhibitory factor in serum in a heat (56° C for 30 min) and storage (4°C for 2–5 days) labile macromolecule (mol. wt 50 000) and requires Ca²⁺ for its effect. The cellular electrical potential difference of the proximal tubular cells was irreversively destroyed and intraluminally perfused trypan blue dye incorporated into the tubular cells after the intraluminal perfusion with serum for 2 min. These observations suggest that lysis of the proximal tubular cells is the mechanism for serum-induced inhibition of proximal tubular isotonic reabsorption.     

Lysis of Trypanosoma brucei by a toxic subspecies of human high density lipoprotein

Trypanosoma brucei brucei is an important pathogen of domestic cattle in sub-Saharan Africa and is closely related to the human sleeping sickness parasites, Trypanosoma brucei gambiense and Trypanosoma brucei rhodesiense. However, T. b. brucei is non-infectious to humans. The restriction of the host range of T. b. brucei results from the sensitivity of the parasite to lysis by toxic human high density lipoproteins (HDL) (Rifkin, M. R. (1978) Proc. Natl. Acad. Sci. U.S.A. 75, 3450-3454). We show in this report that trypanosome lytic activity is not a universal feature of all human HDL particles but rather that it is associated with a minor subclass of HDL. We have purified the lytic activity about 8,000-fold and have identified and characterized the subspecies of HDL responsible for trypanosome lysis. This class of HDL has a relative molecular weight of 490,000, a buoyant density of 1.21-1.24 g/ml, and a particle diameter of 150-210 A. It contains apolipoproteins AI, AII, CI, CII, and CIII, and monoclonal antibodies against apo-AI and apo-AII inhibit trypanocidal activity. In addition to these common apolipoproteins, the particles also contain at least three unique proteins, as measured by sodium dodecyl sulfate-polyacrylamide gel electrophoresis under nonreducing conditions. Treatment of the particles with dithiothreitol resulted in the disappearance of two of the proteins and abolished trypanocidal activity. Two-dimensional gel electrophoresis showed that these proteins were a disulfide-linked trimer of 45,000, 36,000, and 13,500-Da polypeptides and dimers of the 36,000- and 13,500-Da polypeptides or of 65,000- and 8,500-Da polypeptides. Studies on the lysis of T. b. brucei by the purified particle suggest that the lytic pathway may involve the uptake of the trypanocidal subspecies of HDL by endocytosis.