Purification and characterization of mouse liver xanthine oxidase

Xanthine oxidase (EC 1.1.3.22) is purified to homogeneity from mouse liver after induction with bacterial lipopolysaccharide. The enzyme has an apparent molecular weight of 300,000 in its native state and it is suggested to be constituted of two identical subunits of Mr 150,000 each. The isoelectric point is 6.7 and the apparent Km value for xanthine is 3.4 microM. The amino acid composition of mouse xanthine oxidase is quite similar to that of Drosophila xanthine dehydrogenase.     

Effect of prostaglandin A2 on Na+-K+-ATPase in basolateral plasma membrane of rat intestine in vitro inhibition of activation of K+-dependent p-nitrophenylphosphatase by Na+ and ATP

1. The activation of K+-dependent p-nitrophenylphosphatase (EC 3.6.1.7) by both Na+ and ATP in rat intestinal basolateral plasma membrane is inhibited by prostaglandin A2. 2. The drug's inhibition of the activation of the enzyme by both Na+ and ATP is due to a decrease in the affinity of the enzyme for Na+ and in the Vmax of the enzyme. 3. The Ki values for this drug for Na+ and ATP in the activation of the enzyme were 45 and 70 microM, respectively.     

Further Clonal Expansion of T Cells upon Rechallenge of Superantigen Staphylococcal Enterotoxin A

Superantigens are known to induce clonal anergy and/or deletion in reactive T cells peripherally. This study was undertaken to investigate the T-cell status early after exposure to staphylococcal enterotoxin A (SEA) in vivo and in vitro. At the peak of clonal expansion following the administration of 5 μg SEA (i.e., 2 days after the injection), C57BL/6 mice were rechallenged with the same dose of SEA in vivo. The secondary stimulation augmented clonal expansion of the T cells bearing Vβ3 and Vβ11 in both CD4⁺ and CD8⁺ populations. In vitro restimulation of the spleen cells taken from the SEA-primed mice also induced further expansion of the Vβ3⁺ T cells during 2 days of culturing, whereas without restimulation, a marked reduction of Vβ3⁺ T cells occurred. The spleen cells from the SEA-primed mice were hyper-reactive to in vitro restimulation with SEA as measured by ³H-TdR uptake on day 1 of culturing, but augmented proliferation leveled off thereafter. By day 3, the values of ³H-TdR uptake were less than 20% of those of the controls in which spleen cells from native mice were stimulated with SEA in vitro. These results suggest that T cells exposed to SEA in vivo are still capable of proliferating upon SEA rechallenge, but subsequently, the proliferation starts to wane.