A novel hydrogenase has recently been found in methanogenic archaea. It catalyzes the reversible dehydrogenation of methylenetetrahydromethanopterin (CH2=H4MPT) to methenyltetrahydromethanopterin (CHEH4MPT') and H2 and was therefore named H2-forming methylenetetrahydromethanopterin dehydrogenase. The hydrogenasc, which is composed of only one polypeptide with an apparent molecular mass of 43 kDa, does not mediate the reduction of viologen dyes with either Hz or CH2=H4MPT. We report here that the purified enzyme from Methanobacterium thernioautotrophicum exhibits the following other unique properties : (a) the colorless protein with a specific activity or 2000 Uimg (V,,,,,) did not contain iron-sulfur clusters, nickel, or flavins; (b) the activity was not inhibited by carbon monoxide, acetylene. nitrite, cyanide, or azide; (cj the enzyme did not catalyze an isotopic exchange between 'H, and 'H+ ; (d) the enzyme catalyzed the reduction of CHFH4MPT+ with 'H, generating [n2ethylenc-'HH]CH,=H4MPT; and (e) the primary structure contained at most four conserved cysteines as revealed by a comparison of the DNA-deduced amino acid sequence of [he proteins from M . theumuautotrophicum and Methanopyrus kundleri. None of the four cysteines were closely spaced as would be indicative for a (NiFe) hydrogenase or a ferredoxintype iron-sulfur protein.Properties of the H,-forming methylenetetrahydromethanopterin dehydrogenase from Methmobacterium i v d f e i are also described indicating that thc enzyme from this methanogenic archaeon is very similar to the enzyme from M . thermoautotrophicum with respect both to molecular and catalytic properties.

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Abstract:The swelling/deswelling behaviour of microgel particles in the bulk and at the surface was studied and correlated to their mechanical properties. We focused on two kinds of particles: pure PNIPAM and PNIPAM-co-AAc particles. It was shown that the two step volume phase transition found for PNIPAM-co-AAc particles in the bulk disappears after the adsorption at the surface and only a one step transition was identified. The transition temperature increased strongly with increasing the co-monomer content. The dependence of the Young's modulus of the adsorbed microgel particles on the temperature and the co-monomer content was discussed. The investigations were performed via DLS and SFM.

The light‐induced reversible switching of the swelling of microgel particles triggered by photo‐isomerization and binding/unbinding of a photosensitive azobenzene‐containing surfactant is reported. The interactions between the microgel (N‐isopropylacrylamide, co‐monomer: allyl acetic acid, crosslinker: N,N′‐methylenebisacrylamide) and the surfactant are studied by UV‐Vis spectroscopy, dynamic and electrophoretic light scattering measurements. Addition of the surfactant above a critical concentration leads to contraction/collapse of the microgel. UV light irradiation results in trans‐cis isomerization of the azobenzene unit incorporated into the surfactant tail and causes an unbinding of the more hydrophilic cis isomer from the microgel and its reversible swelling. The reversible contraction can be realized by blue light irradiation that transfers the surfactant back to the more hydrophobic trans conformation, in which it binds to the microgel. The phase diagram of the surfactant‐microgel interaction and transitions (aggregation, contraction, and precipitation) is constructed and allows prediction of changes in the system when the concentration of one or both components is varied. Remote and reversible switching between different states can be realized by either UV or visible light irradiation.

SummaryThe filamentous bacterium Streptomyces coelicolor undergoes a complex process of morphological differentiation involving the formation of a dense lawn of aerial hyphae that grow away from the colony surface into the air to form an aerial mycelium. Bald mutants of S. coelicolor, which are blocked in aerial mycelium formation, regain the capacity to erect aerial structures when exposed to a small hydrophobic protein called SapB, whose synthesis is temporally and spatially correlated with morphological differentiation. We now report that SapB is a surfactant that is capable of reducing the surface tension of water from 72 mJ m ¹2 to 30 mJ m ¹2 at a concentration of 50 g ml ¹1 . We also report that SapB, like the surface-active peptide streptofactin produced by the species S. tendae, was capable of restoring the capacity of bald mutants of S. tendae to erect aerial structures. Strikingly, a member (SC3) of the hydrophobin family of fungal proteins involved in the erection of aerial hyphae in the filamentous fungus Schizophyllum commune was also capable of restoring the capacity of S. coelicolor and S. tendae bald mutants to erect aerial structures. SC3 is unrelated in structure to SapB and streptofactin but, like the streptomycetes proteins, the fungal protein is a surface active agent. Scanning electron microscopy revealed that aerial structures produced in response to both the bacterial or the fungal proteins were undifferentiated vegetative hyphae that had grown away from the colony surface but had not commenced the process of spore formation. We conclude that the production of SapB and streptofactin at the start of morphological differentiation contributes to the erection of aerial hyphae by decreasing the surface tension at the colony surface but that subsequent morphogenesis requires additional developmentally regulated events under the control of bald genes.