Reclassification of incompatibility group L (IncL) plasmids.

Plasmids classified as IncL are shown to be incompatible with plasmids of IncM and we propose to reclassify them as IncM.     

Comparative study of methods for the enumeration of total and fecal coliforms in the eastern oyster, Crassostrea virginica.

Violet red bile agar and Coli-Count Sampler (Millipore Corp.) procedures were shown to be acceptable alternatives to the standard most-probable-number method for monitoring relative coliform levels in oysters.     

A hydrogen-deuterium exchange study of the amide protons of polymyxin B by nuclear-magnetic-resonance spectroscopy.

1. Proton magnetic resonance spectra at 270 MHz of polymyxin B, a cationic oligopeptide antibiotic, show the influence of the inorganic counteranion present in solution. 2. Hydrogen-deuterium exchange rates for the amide protons are of two types, depending on whether the anion is monovalent or polyvalent. Polyvalent anions catalyse the acid-catalysed reaction more than the monovalent anions. 3. The structure in solution was monitored using the proton signals of the amides, the phenylalanine aromatic protons, and the leucine methyl and gamma-CH protons in several polymyxin salts. The temperature coefficients of the chemical shifts of the N-H protons are used to identify two beta turns in the cyclic ring of polymyxin B. The variation in chemical shift of the N-H protons, the aromatic protons and the leucine protons are correlated with anionic size and electronegativity.     

Interaction of radical anion probes with glucoamylase I from Aspergillus niger.

The radical anions (SCN)2.- and Br2.- produced during a pulse radiolysis of the respective potassium salts have been used to study the tryptophan residues of the glucoenzyme, glucoamylase I (EC 3.2.1.3.). At neutral pH, Br2.- reacted with the tryptophan residues of glucoamylase I as expected from previous studies of proteins and free amino acids. However, (SCN)2.- at neutral and high pH was surprisingly unreactive towards the native enzyme. Reaction did occur, however, between (SCN)2.- and glucoamylase from which one-third of the covalently bound carbohydrate had been removed, producing a tryptophyl radical. Reaction also occured between (SCN)2.- and glucoamylase I inactivated by treatment with sodium dodecyl sulphate, but the tryptophan residues were not involved. It is concluded from the results that two 'types' of tryptophan residues are found in glucoamylase I; both are attacked by Br2.- but only one type is attacked by (SCN)2.-.     

Purification,properties, and mode of action of hemicellulase I produced by Ceratocystis paradoxa

A culture isolate (CP₂) of the fungal plant pathogen Ceratocystis paradoxa produces at least five extra-cellular hemicellulases when grown on a medium containing a commercial hemicellulose as inducer. One of the five enzymes, hemicellulase I (HC-I), was purified by ammonium sulphate precipitation, ion-exchange chromatography (DEAE-Sephadex and then Cellex-CM), and iso-electric focusing at pH 3–10 and 8–10. HC-I behaves as a single protein on electrophoresis at pH 6.0 and 8.4. The enzyme degrades hemicellulose B (an arabino-4-O-methylglucuronoxylan) and arabinoxylan to arabinose, xylose, xylobiose (Xyl₂; β-D-Xylp-(1→4)-D-Xyl), and a mixture of arabinose-xylose and xylose oligosaccharides (AraXyl_n and Xyl_n, where n  3, 4, or 5). The enzyme is deduced to be an endo-enzyme. Xylotetraose (Xyl₄) was the lowest homologue of the xylose oligosaccharides attacked, yielding xylobiose and xylotriose (Xyl₃) only. A mechanism is postulated for this reaction. AraXyl₂AraXyl₅ were slowly hydrolysed to arabinose and the respective xylose saccharide (Xyl₂Xyl₅), and thence to Xyl₂ and Xyl₃. Hydrolysis of the arabinofuranosyl linkage probably does not occur at the same active site as for the xylose oligosaccharides. Hemicellulose B fractions from different sources appeared to be degraded by HC-I. The enzyme showed optimum activity at pH 5.5 and 40°, and K_m was 4.24 mg of hemicellulose/ml.