含锰固氮酶组分Ⅰ蛋白的纯化和特性

棕色固氮菌（Azotobacter vinelandii Lipmann)突变种UW3能在无Mo的无氨培养基中固氮生长,低浓度的Mn对UW3突变种生长有促进作用,从在Mn中生长的UW3菌体中分离得到的部分纯固氮酶组分Ⅰ蛋白含量有Mn和Fe原子（Fe/Mo/Mn为10．41：0．19：1．00）并有OP MoFe蛋白一半的还原乙炔和质子的活性。这种蛋白的吸收光谱和圆二色谱与MoFe蛋白存在明显的差异,含Mn蛋白的亚基分子量都与MoFe蛋白的α亚基相近。初步结果表明,这种含Mn蛋白可胡是一种固氮酶组分Ⅰ蛋白。     

Inhibition by 6-O-tosyl galactosides of beta-galactoside phosphorylation and transport by the lactose phosphotransferase system of Staphylococcus aureus.

The effect of various galactose derivatives, substituted at C-6, on the phosphoenolpyruvate:beta-galactoside phosphotransferase system of Staphylococcus aureus was studied. Cells were grown by an improved procedure, which resulted in a 5- to 10-fold increase in cell yield. The four protein components of the system were separated. A membrane fraction containing negligible levels of the soluble components was prepared by alternate cycles of sonic treatment and differential centrifugation. The in vitro system reconstituted from these fractions was used to test the ability of the galactose derivatives to inhibit the phosphorylation of lactose analogs, under conditions where the membrane-bound component, Enzyme IIlac, was rate limiting. Derivaites in which the hydroxyl group of C-6 was missing, or replaced by a fluoro, O-methyl, or carboxyl group had no affinity for Enzyme IIlac, as judged by their inability to inhibit phosphorylation. Surprisingly, derivatives containing arylsulfonyl groups at C-6 were potent inhibitors; the O-tosyl compound has an apparent affinity five times that of galactose. The arylsulfonyl substitution in an absolute requirement; neither O-benzyl or O-methanesulfonyl derivatives were inhibitory. The specificity of the inhibition by tosyl derivatives parallels that of unsubstituted substrates; tosyl galactosides of the beta configuration were inhibitory, but those of the alpha configuration were not. The tosyl derivatives also strongly inhibited the uptake of lactose analogs into whole cells; the requirement for the arylsulfonyl moiety was again observed. The chemical analogy between the tosyl galactosides and possible intermediates in the transport-phosphorylation step catalyzed by Enzyme IIlac provides a possible explanation for the unexpected properties of these derivatives.     

Actin depolymerization in the cyclic AMP-stimulated toad bladder epithelial cell, determined by the DNAse method

Previous studies with the rhodamine phalloidin binding assay have shown that antidiuretic hormone and 8-Br-cAMP rapidly depolymerize F-actin in toad bladder epithelial cells. We have extended these studies with DNAse inhibition assay and have found that in isolated epithelial cell suspensions, G-actin increases from 37 to 56% of total actin following 8-br-cAMP stimulation. The G-actin concentration in the epithelial cell greatly exceeds its critical concentration, indicating the requirement for a G-actin sequestering protein or proteins in this system.