Fungal contamination and mycotoxin-producing potential of dried beans

A total of 604 samples of about 7 different types of beans was examined to determine their mycological profiles, and suitability for use as solid substrates for mycotoxin production.All of the samples were collected from bean jam makers in Tokyo by the official food examiners.Genera Penicillium and Aspergillus were predominant, and genus Wallemia was also found commonly in all types of beans.Mycotoxin-producing Aspergillus strains were isolated from 52 samples of beans, approximately 9% of the total. The highest incidence of toxigenic Aspergillus (14.1%) was found in kidney beans. Red beans and peas inoculated with Aspergillus ochraceus were found to produce about 7 to 8 times more toxin than was obtained in a liquid medium, and red beans inoculated with A. versicolor produced more toxin than was obtained in yeast extract sucrose broth. Green peas inoculated with Fusarium graminearum produced about 8 times more T-2 toxin than was obtained in 1% peptone containing Czapek solution under comparable culture conditions.     

A sulfotransferase model: Covalent participation of a macrocyclic oxime in the hydrolysis of 2,4-dinitrophenyl sulfate

The liberation of 2,4-dinitrophenolate ion from 2,4-dinitrophenyl sulfate (DNPS) in aqueous organic solvent with 0.1 N sodium hydroxide was accelerated upon addition of an equimolar amount of Oxime-I (10-hydroxy-11-hydroxyimino[20]-paracyclophane) to the sulfate ester. Oxime-I was found to undergo covalent participation at the oxime group to afford oxime O-sulfonate. The rate acceleration with Oxime-I was larger than that with β-CD (cycloheptaamylose). The catalytic efficiency of Oxime-I has been ascribed primarily to the tighter inclusion of the substrate ester into the more hydrophobic Oxime-I cavity provided by the effective apolar paracyclophane skeleton, as well as to the greater nucleophilicity of the oxime group than of the hydroxyl group in β-CD. Consequently, Oxime-I may be considered as a conventional model for arylsulfatases and sulfotransferases, providing the effective binding process for the substrate.     

Break points in Arrhenius plots of the Hill reaction of spinach chloroplast fragments in the temperature range from -25 to 25?C

The relationship between temperature and 2,6-dichlorophenolindophenol(DPIP) photoreduction activity in chloroplast fragments isolatedfrom spinach grown at different temperatures was investigatedin the temperature range from –25 to 25?C. Two break points in the slope of the Arrhenius plot of the Hillreaction were observed at –9 and 11?C in chloroplast fragmentsisolated from spinach grown at low temperatures (0–10?C).These breaks were not affected by an uncoupler. In chloroplastfragments from spinach grown in a higher temperature range (10–30?C),only one break point was observed at –9?C. The other breakpoint at around 10?C appeared after treatment with detergent.Both break points were completely abolished by fixing the chloroplastfragments with glutaraldehyde. The break at around 10?C in chloroplast fragments isolated fromspinach grown at lower temperature was interpreted as due toacclimation rather than chilling sensitivity. (Received September 6, 1977; )     

Metronidazole-induced susceptibility of adult mice to intestinalClostridium botulinum colonization

Clostridium botulinum type A spore challenges were given orogastrically to adult mice that had been treated with metronidazole. The organism multiplied in the intestinal tract for up to five days if it was administered 9–48 h after the last dose of metronidazole. The known antibacterial spectrum of metronidazole indicated that obligate anaerobic bacteria are important in the natural resistance of adult mice to colonization byC. botulinum, but treatment with the antimicrobial agent did not reduce the number of these bacteria in the cecum and colon.     

Visualization of the nature of protein folding by a study of a distance constraint approach in two-dimensional models

A distance constraint approach is applied to two-dimensional models of proteins in order to visualize the nature of protein folding and to examine the relative roles of different ranges of interaction. Three different native structures (I, II, and III) are considered; they have two different kinds of residues, viz., hydrophobic and hydrophilic, and different sequences of these residues. We examine how the distance constraint approach functions in the prediction of protein folding when we know the sequence of the residues, the (fixed) bond lengths, the mean distances between residues i and i + 2, and i and i + 3, and the mean distances for hydrophobic–hydrophobic, hydrophobic–hydrophilic, and hydrophilic–hydrophilic contacts between residues i and i + j, where j ≥ 4. This approach involves optimization of an object function with respect to 98 variables and is not free of the multiple-minimum problem. The optimization is always terminated if the chain is entangled and/or the segments (residues) are packed too compactly to move. In order to escape from such situations and to take the excluded-volume effect into account, a Monte Carlo method is used after the optimization is trapped in local minima. Success in the prediction of folding is found to depend on the starting conformations and on the native conformations. Fair success is obtained in predicting the helix-like structure in protein I and the overall structure of protein III, but not the β-like structures of proteins I and II. Insofar as the prediction of the structure of protein III is reasonable, it appears that some sequences of residues produce greater constraints on their conformations than others, if one considers only the hydrophobic and hydrophilic nature of the residues. These results imply that, in the folding of real proteins in three dimensions, the competition for hydrophobic (and hydrophilic) residues for inside (outside) positions in the molecule probably constitutes a necessary but not a sufficient condition to form and stabilize the native structure. The failure to predict the structure of protein II, and part of that of protein I, suggests that there are two types of long-range interactions. One (which we considered here) is nonspecific (i.e., is defined only in terms of contacts between residues of the same or different polarity) and acts at any stage of protein folding; the other (which we did not consider here) is a specific interaction between residues in pairs and contributes only when the residues in the specific pair take on the native conformation. Presumably, incorporation of such specific long-range interactions, together with the nonspecific ones, is necessary for successful protein folding, using the distance constraint approach.     

Nucleotide sequence of the genes for β and ε subunits of proton-translocating ATPase from Escherichia coli

The 1855-nucleotide long DNA sequence of part of the gene cluster for the proton-translocating ATPase from $\text{E. coli}$ was determined by the method of Maxam-Gilbert. The sequence covers the genes for the β and ε subunits of F₁ along with the flanking region. The amino acid sequence of these subunits deduced from the nucleotide sequence indicates that the β and ε subunits have 459 and 138 amino acids, respectively. The possible secondary structure of the both subunits was estimated from the deduced primary structures. A possible nucleotide binding site in the β subunit is also discussed on the basis of the primary and secondary structures. The codons used in the genes for all the components of F₁F₀ were different in different genes, suggesting that the amount of each subunit in the F₁F₀ is determined to some extent on a translational level.