Kinetics, equilibria, and modeling of the formation of oligosaccharides from D-glucose with Aspergillus niger glucoamylases I and II

Near-homogeneous forms of glucoamylases I and II, previously purified from an industrial Aspergillus niger preparation, were incubated with D-glucose at a number of temperatures and pH values. Kinetics and equilibria of the formation of alpha,beta-trehalose, kojibiose, nigerose, maltose, isomaltose, panose, and isomaltotriose, which with isomaltotetraose were the only products formed, were determined. There was no difference in the abilities of GA I and GA II to form these products. Activation energies for the formation of maltose and panose were lower than those of the other Oligosaccharides. Relative rates of oligosaccharide production based on glucoamylase hydrolytic activity did not vary significantly between pH 3.5 and 4.5 but were lower at pH 5.5. Maltose was formed much faster than any other product. Equilibrium concentrations at higher dissolved solids concentrations decreased in the order isomaltose, isomaltotriose, kojibiose, nigerose, maltose, alpha, beta-Mrehalose, panose, and isomaltotetraose. They were not appreciably affected by changes in temperature or pH. A kinetic model based on adsorption of D-glucose and the seven di- and trisaccharides by the first three glucoamylase subsites was formulated. Oligosaccharide formation was simulated with the model, using equilibrium data gathered for this article and subsite binding energies and kinetic parameters for oligosaccharide hydrolysis measured earlier. Agreement of simulated and actual oligosaccharide formation data through the course of the reaction was excellent except at very high solid concentrations.     

Cloning a promoter that puts the expression of tetracycline resistance under the control of the regulatory elements of the mer operon

We have sub-cloned from the Eco RI-H fragments of the IncFII plasmid R100 a 260-bp EcoRI fragment, using the promoter-cloning vehicle, pBRH4, (The Inc FII plasmid codes for the mer operon, and pBRH4 expresses tetracycline resistance only when the deleted tet promoter has been replaced by another sequence that can serve as a promotor). With the 260-bp fragment inserted, the derivative plasmid, pFB4, directs the expression of tetracycline resistance only if there is a second plasmid in the strain that carries the merR-positive regulatory element. Under these conditions, the level of tetracycline resistance is directly proportional to the concentration of Hg2+ present in the medium. The 260-bp fragment also allows low-level constitutive expression of tet resistance when transactivated with merR mutants that have a "micro-constitutive" phenotype. The 260-bp mer promoter fragment contains a single HincII site; there is also but one HincII site in the EcoRI-H fragment of R100 from which the promoter fragment was derived. Restriction analysis of purified Eco RI-H DNA shows that the single HincII site is at 550 bp from the "right"terminus of the IS1b element, which is also present in the EcoRI-H fragment. Because of its biological activity and its location within the "H" fragment, this promoter is very likely a promoter for the structural genes of the operon.     

Influence of ground cover and herbicide treatments onTetranychus urticae populations in peach orchards

Two-spotted spider mites,Tetranychus urticae Koch, were sampled in peach orchards to quantify abundance in trees over different types of ground cover to document the dispersal of mites from orchard-floor plants to trees. Mite populations developed more quickly and with higher densities in trees over ground cover compared to bare ground, and specifically over covers of predominantly narrowleaf vetch,Vicia angustifolia Reichard. Orchard floor plants such asVicia, Geranium, Lamium, andLepidium contained relatively high densities of mites during early spring, and may have formed the source for later peach-tree infestation.Paper no. 11982 of the Journal Series of the North Carolina Agricultural Research Service, Raleigh, NC 27695-7643, U.S.A.     

Rapid manual sequencing of multiple peptide samples in a nitrogen chamber.

Automatic protein sequenators are very expensive. Most laboratories must rely on slower manual methods. This paper describes an inexpensive nitrogen chamber in which multiple peptide samples may be sequenced manually and yet rapidly. The nitrogen environment keeps samples free from oxygen, water vapor, and dust. A complete, simple procedure for degrading peptides is also included. From six to twelve peptide samples may be degraded through one cycle of Edman degradation in a single morning. Several pieces of new equipment and procedures are described which simplify the manipulations involved in protein sequencing.     

Parental and sib likelihoods in genealogy reconstruction

Estimation of genealogical relationships from genetic data provides an approach to answering many questions of population biology. In this estimation problem, previous work has shown that bilateral relatives such as full sibs may be more likely parents than the true parent individuals. This paper investigates the source of this paradox, and the circumstances under which it may arise. Alternative approaches to inferring parentage are proposed; these involve analysis of the distributions of log-likelihood statistics and of the bivariate distribution of sib and parent log-likelihoods. A Bayesian approach may also be superposed on the likelihood analysis, enabling any prior knowledge of the population to be incorporated.