Coenzyme F430 as a possible catalyst for the reductive dehalogenation of chlorinated C1 hydrocarbons in methanogenic bacteria

Corrinoids, such as aquocobalamin, methylcobalamin, and (cyanoaquo)cobinamide, catalyze the reductive dehalogenation of CCl4 with titanium(III) citrate as the electron donor [Krone et al. (1989) Biochemistry 28, 4908-4914]. We report here that this reaction is also effectively mediated by the nickel-containing porphinoid, coenzyme F430, found in methanogenic bacteria. Chloroform, methylene chloride, methyl chloride, and methane were detected as intermediates and products. Ethane was formed in trace amounts, and several as yet unidentified nonvolatile compounds were also generated. The rate of dehalogenation decreased in the series of CCl4, CHCl3, and CH2Cl2. With coenzyme F430 as the catalyst, the reduction of CH3Cl to CH4 proceeded more than 50 times faster than with aquocobalamin. Cell suspensions of Methanosarcina barkeri were found to catalyze the reductive dehalogenation of CCl4 with CO as the electron donor (E'0 = -0.524 V). Methylene chloride was the main end product. The kinetics of CHCl3 and CH2Cl2 formation from CCl4 were similar to those with coenzyme F430 or aquocobalamin as catalysts and titanium(III) citrate as the reductant.     

Water Balance in Cucumis Plants, Measured by Nuclear Magnetic Resonance, I

In this paper we demonstrate the study of plant water balanceby the non-invasive measurement of tissue water content andwater flow using proton nuclear magnetic resonance (NMR). Sapvelocity and flux were measured independently in the presenceof an excess of stationary tissue water. The instrumentationdescribed allows automated and unattended measurement of flow-and water content-variables in a well-defined region of theplant over periods of several days, with a time resolution betweensuccessive measurements of c. 5 s. Using this apparatus theeffect of changes in light intensity (day/night rhythm) andrelative humidity on stem tissue water content as well as onthe velocity and flux of xylem sap in the stem were investigatedin a cucumber plant. The results are in agreement with predictionsfrom a simple model for plant water balance, which is basedon water potential, flow rate and resistance to flow. As longas only transpiration is varied, flow rate and water content(or potential) are affected in opposite ways as demonstratedin this paper. In contrast, the model predicts that changesin uptake (resulting from changes in, for example, root resistance)will induce changes in water content and flow in the same direction.An experimental verification of this prediction is given ina subsequent paper, where, in addition, the NMR results arecompared to those obtained with a dendrometer. Key words: Water balance model, Cucumis sativus L., flow, water content, NMR, water balance measurement     

The salivary flow rate and composition of whole and parotid resting and stimulated saliva in young and old healthy subjects

Resting and stimulated whole and parotid salivary composition and flow rate were examined in 63 healthy volunteers. No significant differences were found between the young and old in secretion rates and salivary concentrations of sodium, potassium, calcium, magnesium, and total protein. The activity of amylase in the resting and stimulated parotid saliva was significantly lower in the old.     

Hydrolysis of RNA to 5′-nucleotide by seed sprouts,particularly malt sprouts

Conditions for the efficient conversion of commercial RNA to nucleoside 5′-monophosphate by means of a phosphodiesterase in malt sprouts have been determined. A comparison of the enzyme content of the rootlets, stems, and kernels of various plant seedlings, including barley, rye, oat, wheat, rice, and beans shows maximum amounts in the rootlets, and minimum quantities in the ungerminated kernels. Of all the seedlings tested, (mung bean, soy bean, oat, wheat, rice, barley) barley gave the highest conversion of RNA to 5′-nucleotides. Commercial malt sprouts prepared from 6 different malted barleys including 2-rowed and 6-rowed samples all showed about the same amount of phosphodiesterase content. Besides phosphodiesterase, other enzymes capable of hydrolyzing RNA and 5′-nucleotides were found in sprouts. These included 3′-phosphodiesterases, 5′-nucleotidases, and nucleosidases. By carefully pretreating both extracts and the solid sprouts at elevated temperatures for a limited time and by the addition of minimum amounts of Zn⁺², the action of these undesirable enzymes was either effectively destroyed or minimized so that the production of 5′-nucleotides was maximized. It was found that suspensions of appropriately washed and treated barley malt rootlets are substantially more effective than aqueous extracts for converting RNA to 5′-nucleotides.     

DEVELOPMENTAL STUDIES OF THE DIPTERAN SALIVARY GLAND : II. DNase Activity in Chironomus thummi

The deoxyribonuclease (DNase) activity of the dipteran (Chironomus thummi) salivary gland, measured both enzymatically and immunochemically, increases about 7-fold with the onset of metamorphosis. The increase in DNase activity occurs at a time when the activities of other enzymes and the total protein content are decreasing. The increased DNase activity is followed by glandular destruction. It is suggested that the alterations of this activity may be regulated by the activities of specific chromosomal sites, and that the enzyme may, at least in part, account for the glandular destruction observed at the time of increased enzyme activity.