A mechanism for the elimination of the female gamete centrosome in Drosophila melanogaster.

An important feature of fertilization is the asymmetric inheritance of centrioles. In most species it is the sperm that contributes the initial centriole, which builds the first centrosome that is essential for early development. However, given that centrioles are thought to be exceptionally stable structures, the mechanism behind centriole disappearance in the female germ line remains elusive and paradoxical. We elucidated a program for centriole maintenance in fruit flies, led by Polo kinase and the pericentriolar matrix (PCM): The PCM is down-regulated in the female germ line during oogenesis, which results in centriole loss. Perturbing this program prevents centriole loss, leading to abnormal meiotic and mitotic divisions, and thus to female sterility. This mechanism challenges the view that centrioles are intrinsically stable structures and reveals general functions for Polo kinase and the PCM in centriole maintenance. We propose that regulation of this maintenance program is essential for successful sexual reproduction and defines centriole life span in different tissues in homeostasis and disease, thereby shaping the cytoskeleton.

Induction and carbon catabolite repression in the biosynthesis of beta-amylase by Bacillus megaterium B6.

Biosynthesis of extracellular beta-amylase in Bacillus megaterium B6 was induced by starch, although maltodextrin was found to be the actual inducer. Amongst the carbon sources tested, glucose was found to be the most potent repressor and when added exogenously to a starch-induced culture it brought about an immediate fall in enzyme synthesis through carbon catabolite repression. The repression was not overcome after the fall of glucose concentration in the culture medium below a critical level. This "catabolite repression" exerted by glucose was partially relieved by exogenous cyclic guanosine monophosphate (CGMP) and its dibutyryl derivative. On the other hand, guanosine monophosphate (GMP) was found to restore the original extent of enzyme synthesis in glucose repressed cells.

Biochemical approaches of increasing thermostability of beta-amylase from Bacillus megaterium B6.

Studies on the irreversible thermoinactivation of beta-amylase from Bacillus megaterium B6 exposed to 60 degrees C revealed that the deactivation mechanism probably results from the oxidation of thiols present at the active site of the enzyme. Several attempts were made to increase its thermostability, which indicated that Mn2+ played a key role in determining thermostability and partially reactivating the inactivated enzyme. Immobilization of beta-amylase through gel-entrapment and covalent crosslinking brought about a remarkable increase in thermotolerance with about a 14-fold increase in catalytic half-life.

Saccharification of indigenous starches by ß-Amylase of Bacillus megaterium.

Extracellular ß-amylase from Bacillus megaterium converted indigenous starches from low-grade, raw materials to maltose. The extent of saccharification was higher with gelatinized starches than the raw material. For the gelatinized starches the optima for saccharification were pH 6.9 and 60°C.

Chaos, symmetry, and self-similarity: exploiting order and disorder in mixing processes.

Fluid mixing is a successful application of chaos. Theory anticipates the coexistence of order and disorder-symmetry and chaos-as well as self-similarity and multifractality arising from repeated stretching and folding. Experiments and computations, in turn, provide a point of confluence and a visual analog for chaotic behavior, multiplicative processes, and scaling behavior. All these concepts have conceptual engineering counterparts: examples arise in the context of flow classification, design of mixing devices, enhancement of transport processes, and controlled structure formation in two-phase systems.

Taxonomic relationship of some members of Azotobacteraceae based on their protein profiles.

Analysis of protein profiles of the members of Azotobacteraceae suggests that the genus Azotobacter consists of a heterogeneous group of bacteria, of which Azotobacter beijerinekii should possibly be separated to a new genus. Azomonas agilis and Azomonas macrocytogenes are only 26 percent related to each other.

Production, purification, and characterization of xylanase from a hyperxylanolytic mutant of Aspergillus ochraceus.

Enhancement of the productivity of xylanase and beta-xy-losidase of Aspergillus ochraceus was investigated by multistep mutagenesis. The spores of the wild strain were subjected to UV and N-methyl-N-nitro-N-nitro-soguanidine (NTG). The hyperxylanolytic mutant (NG-13), which showed good clearing on the surface of the xylan-agar plate, secretes xylanase and beta-xylosidase at high levels during growth on commercial xylan and on agricultural wastes. Both liquid and solid state cultures were employed in the study for enzyme production. The xylanase from NG-13 was purified to homogeneity by ammonium sulfate precipitation and gel filtration. This purified enzyme showed a pH optimum of 6.0 and was stable in the range of pH 5 to 10. Prolonged stability of the enzyme was observed at 45 degrees C though its activity was maximal at 50 degrees C. The molecular weight of the enzyme was estimated to be 4.3 x 10(4) by SDS-polyacrylamide gel electrophoresis and 5 x 10(4) by gel filtration on Sephadex G-75. The kinetic data showed that the K(m) and V(max) values for xylan were 1 x 10(-3)M and 19.6 mumol/ min/mg protein, respectively. The enzyme was both more active and thermostable in the presence of K(+)and was inactivated by thiol reagents such as Hg(2+), p-hydroxymercuribenzoate (PHMB), 3', 5'-dithiobis (2'-nitrobenzoic acid) (DTNB), and N-ethylmaleimide (NEM).