Investigation of the operational stabilities and kinetics of glucoamylase immobilized on alkylamine derivatives of titanium(IV)-activated porous inorganic supports

Glucoamylase (exo-1,4-α-d-glucosidase, EC 3.2.3.1) was coupled to several porous silica matrices by an improved metal-link/chelation process using alkylamine derivatives of titanium(IV)-activated supports. In order to select the titanium activation procedure which gave stable enzyme preparations, long-term stability tests were performed. The immobilized glucoamylase preparations, in which the carrier was activated to dryness with a 15% w/v TiCl₄ solution, displayed very stable behaviour, with half-lives of ～60 days. The optimum operating conditions were determined for these preparations. There are significant differences between the behaviour of the immobilized enzyme and the free enzyme. The apparent K_m increased on immobilization due to diffusional resistances. The pH optimum for the immobilized preparation showed a slight shift to acid pH relative to that of the soluble enzyme. Also, the optimum temperature descreased to 60°C after immobilization. In order to test Michaelis-Menten kinetics at high degrees of conversion, time-course analysis of soluble starch hydrolysis was performed. It was observed that simple Michaelis-Menten kinetics are not applicable to the free/immobilized glucoamylase-starch system at high degrees of conversion.     

Phenotypic changes in the chemistry of Aspergillus nidulans: Influence of culture conditions on mycelial composition

A quantitative study was made of macromolecular (nucleic acids, protein), carbohydrate and mineral (magnesium, potassium and phosphorus) components of Aspergillus nidulans in glucose limited chemostat cultures, under varying conditions of dilution rate, temperature, pH and NaCl concentration.The overall mineral content showed greatest variation in response to changes in culture salinity, which also affected the mycelial carbohydrate content. Concomitant and opposite changes in the conent of cations and carbohydrates under conditions of increasing salinity may be interpreted in terms of mycelial osmoregulation. Slight variations in DNA content but gross fluctuations in the level of RNA were noted under the different cultural conditions examined. Co-ordinate changes in RNA and Mg²⁺ contents were evident only under certain conditions: dilution rate from 0.05–0.07 h^-1 or temperature from 22–30° C. The constant molar stoichiometry between RNA and Mg²⁺ characteristic of unicellular microorganisms was not a feature of fungal growth. The protein content was most affected by shifts of temperature and reached minimal values at 25 and 50° C.The growth environment had a marked influence on the protein synthesising activity of RNA, which increased eightfold as the dilution rate was increased from 0.02–0.175 h^-1, doubled within the temperature range 20–30° C and fell by 50% between 40 and 50° C. These observations are discussed in the context of the constant ribosomal efficiency in protein synthesis hypothesis.     

Parameter identification of the calvin photosynthesis cycle

Summary This article is concerned with the determination of kinetic parameters of the Calvin photosynthesis cycle which is described by seventeen nonlinear ordinary differential equations. It is shown that the task requires dynamic data for several sets of initial conditions. The numerical technique is based upon an algorithm for non-linear optimization and Gear's numerical integration scheme for stiff systems of differential equations. The sensitivity of the parameters to noise in the data is tested with a method adapted from Rosenbrook and Storey. A preliminary set of parameters has been obtained from a preliminary set of experimental data. The numerical methods are then tested with synthetic data derived from these parameters. The mathematical model and the results obtained in the simulation are used as an aid in designing new experiments.     

On the possible role of organic melanoidin polymers as matrices for prebiotic activity

Summary One of the major diagenetic pathways of organic matter in recent sediments involves the condensation of cellular constituents, particularly amino acids and sugars, into insoluble melanoidin-type polymers. These polymers consist mainly of humic and fulvic acids and make up the major part of the organic carbon reservoir in recent sediments. We suggest that a similar set of reactions between abiotically formed amino acids and sugars, and more generally between aldehydes and amines, occurred on a large scale in the prebiotic hydrosphere. The rapid formation of this insoluble polymeric material would have removed the bulk of the dissolved organic carbon from the primitive oceans and would thus have prevented the formation of an "organic soup".Melanoidin polymers have several properties which make them attractive hypothetical precursors of contemporary oxidation-reduction coenzymes: 1. they contain heterocyclic nitrogen compounds similar to the nitrogenous bases; 2. they contain a high concentration of stable free radicals; and 3. they tend to concentrate those heavy metals which play prominent roles in contemporary enzymic redox processes. The prebiotic formation of similar polymers could, therefore, have provided the starting point for a basic class of biochemical reactions.We suggest that the prebiotic scenario involved chemical and protoenzymic reactions at the sediment-ocean interface in relatively shallow waters and under conditions not much different from those of the recent environment.On leave from the Isotope Department, Weizmann Institute of Sciences, Rehovot, Israel. This is the address for reprint requests.On leave from the Department of Cell and Molecular Biology, San Francisco State University, San Francisco, California.On leave from the Department of Biophysics, University of Houston, Houston, Texas.     

Lumi-mestranol and epi-lumi-mestranol.

Treatment of lumi-estrone 3-methyl ether (I) with acetylene gave the C-17-epimeric compounds lumi-mestranol (3-methoxy-17 alpha-ethynyl-13 alpha-estra-1,3,5(10)-trien-17 beta-ol, III ) and epi-lumi-mestranol (3-methoxy-17 beta-ethynyl-13 alpha-estra-1,3,5(10)-trien-17 alpha-ol, IV). The structures of the two isomers were assigned on the basis of their molecular rotations and shift-reagent experiments in the NMR. The irradiation of estrone 3-methyl ether (II) to provide compound I was investigated in two solvent systems. Minor products of these reactions were the seco-steroids VII, VIII and X.     

New Pyrimidine Cyclonucleosides with Hydrogenated Aglycones: Synthesis and X-Ray Structures

Abstract

Acid catalysed transformations of (6S)-6,5′-anhydro-6-hydroxy-1-(2′,3′-O-isopropylidene-β-D-ribofuranosyl)hexahydropyrimidine-2-thione are studied. (6R)-6,2′-anhydro-6-hydroxy-1-(α-D-ribofuranosyl)hexahydropyrimidine-2-thione was formed as a thermodynamically stable product. Two intermediates, (6S)-6,5′-anhydro-6-hydroxy-1-(β-D-ribofuranosyl)hexahydropyrimidine-2-thione and 6-hydroxy-1-(D-ribosyl)hexahydropyrimidine-2-thione and products of cleavage of glycosidic bond were identified in the reaction mixtures. Results of X-ray structural determination of the synthesised nucleosides are presented.     

CONFERENCE ANNOUNCEMENTS

ABSTRACT

In most mammals, adults produce relatively low frequency vocalizations compared to those of juveniles. This rule is not maintained however at least in four species of ground squirrels, whose juveniles call at the adult's fundamental frequency. These findings have been obtained however with separate sets of juveniles and adults and no data is available concerning the ontogeny linked to these differences. Here we analyze the acoustic structure of alarm calls of the same Yellow Spermophilus fulvus and Speckled S. suslicus ground squirrel individuals, recorded as pups and as adults after hibernation. We found the fundamental frequencies of adults within the same frequency ranges as those of pups, in spite of the significant difference in body mass. In ground squirrels, severing the relationship between body size and call frequency removes some vocal cues to age. We discuss some functional hypotheses advanced to explain manipulations with fundamental frequencies in ground squirrels and other animals, and suggest the lack of data for discussing the mechanisms of such vocal tuning.     

Encapsulation and Permeability Characteristics of Plasma Polymerized Hollow Particles

In this protocol, core-shell nanostructures are synthesized by plasma enhanced chemical vapor deposition. We produce an amorphous barrier by plasma polymerization of isopropanol on various solid substrates, including silica and potassium chloride. This versatile technique is used to treat nanoparticles and nanopowders with sizes ranging from 37 nm to 1 micron, by depositing films whose thickness can be anywhere from 1 nm to upwards of 100 nm. Dissolution of the core allows us to study the rate of permeation through the film. In these experiments, we determine the diffusion coefficient of KCl through the barrier film by coating KCL nanocrystals and subsequently monitoring the ionic conductivity of the coated particles suspended in water. The primary interest in this process is the encapsulation and delayed release of solutes. The thickness of the shell is one of the independent variables by which we control the rate of release. It has a strong effect on the rate of release, which increases from a six-hour release (shell thickness is 20 nm) to a long-term release over 30 days (shell thickness is 95 nm). The release profile shows a characteristic behavior: a fast release (35% of the final materials) during the first five minutes after the beginning of the dissolution, and a slower release till all of the core materials come out.