Decomposition of urea by size-fractionated planktonic community in a eutrophic reservoir in Japan

Free bacterial populations were separated from an intact planktonic community in water of a eutrophic reservoir in Japan by filtration through Whatman GF/ C glass fiber filters (mean porosity 1.2 µm). Urea decomposition by the free bacterial populations and the intact planktonic community was determined in six different months.The separated free bacteria apparently did not take part in urea-decomposition in waters of the reservoir through the year: the number of free heterotrophic bacteria increased during the urea-decomposition experiments, however, the concentration of urea did not decrease. Whereas, in five cases out of six, urea was decomposed by the intact planktonic community. Probably, phytoplankton were responsible for most of the urea-decomposition. On the assumption that the decomposition of urea obeyed first-order kinetics, rate constants were calculated to be 0.00–0.63 day^–1 with a mean value of 0.21 day^–1.     

Inhibition of the synthesis of microbial cellulose by coumarin

Coumarin, a specific inhibitor of the biosynthesis of celluloseof higher plant cell walls, inhibited the cellulose formationof Acetobacter xylinum. The degree of inhibition reached 55%in the presence of 1 mM coumarin, which causes 70% inhibitionin the case of plant cellulose. (Received April 12, 1976; )     

{beta}-1,4-Glucan occurring in homogenate of Phaseolus aureus seedlings. Possible nascent stage of cellulose biosynthesis in vivo

A small amount of cytoplasmic ß-1,4-glucan, whichmight be involved in the synthesis of cellulose in the cellwall, was found in the homogenate prepared from the hypocotylsof seedlings of Phaseolus aureus. Upon hydrolysis by cellulaseof the 20,000?g pellet from the cytoplasmic fraction of segmentsincubated in a [¹⁴C]-glucose solution, [¹⁴C]-cellobiose wasproduced, with specific radioactivities 3 to 10 times greaterthan those of the cellobiose from cellulose in the cell wallat various incubation periods. The incoporation of radioactivityfrom [¹⁴C]-glucose into this cytoplasmic ß-1,4-glucanwas therefore faster than that into cellulose constituting thecell wall. Hence, it seemed that the former ß-1,4-glucancould be turned over. To examine whether the- cytoplasmic ß-1,4-glucanis carried by some subcellular components, cytoplasmic ß-1,4-glucanin the cell was fractionated by differential centrifugation,two enzyme activities being measured as the markers of subcellularcomponents. The distribution of ß-1,4-glucan was similarto that of UDPG-glucosyltransferase activity but not to thatof IDP-ase activity. The result suggests that the cytoplasmicß-1,4-glucan has some relation to plasma membranes. Coumarin, known as a specific inhibitor for the biosynthesisof cellulose in plant cells, was shown to inhibit the incorporationof radiocarbon from [¹⁴C]-glucose into cytoplasmic ß-1,4-glucanto the same extent as that into cellulose in the cell wall ofthe hypocotyls. ¹ Present address: Department of Biological Science, TohokuUniversity, Kawauchi, Sendai 980, Japan. (Received May 31, 1976; )     

A demonstration of energy transfer from photosystem II to photosystem I in chloroplasts

Photosystem I activity of Tris-washed chloroplasts was measured at room temperature as the rate of photoreduction of NADP and as the rate of oxygen uptake mediated by methyl viologen in both cases using dichlorophenolindophenol plus ascorbate as the source of electrons for Photosystem I. With both assay systems the rate of electron transport by Photosystem I was stimulated approx. 20 % by the addition of 3-(3,4-dichlorophenyl)-1, 1-dimethylurea which caused the Photosystem II reaction centers to close. Photosystem I activity of chloroplasts was measured at low temperature as the rate of photooxidation of P-700. Chloroplasts suspended in the presence of hydroxylamine and 3-(3,4-dichlorophenyl)-1, 1-dimethylurea were frozen to ?196 °C after adaptation to darkness or after a preillumination at room temperature. The Photosystem II reaction centers of the frozen dark-adapted sample were all open; those of the preilluminated sample were all closed. The rate of photooxidation of P-700 at ?196 °C with the preilluminated sample was approx. 25 % faster than with the dark-adapted sample. We conclude from both the room temperature and the low temperature experiments that there is greater energy transfer from Photosystem II to Photosystem I when the Photosystem II reaction centers are closed and that these results are a direct demonstration of spillover.     

Utilization of hexoses in fission yeast, Schizosaccharomyces pombe II. Rate of consumption and intracellular accumulation of glucose and mannose

The rates of the utilization of glucose and mannose in Schizosaccharomycespombe were determined using glucose-grown cells. The rate ofaerobic fermentation in the medium containing glucose was notaffected by the addition of mannose. In contrast, CO₂ evolutionin the mannose medium was greatly enhanced by the addition ofglucose, showing nearly the same rate as the glucose medium.The rate of glucose consumption was much higher than that ofmannose. In a medium containing both sugars, the rates of consumptionof glucose and mannose interfered with each other, the mannoseconsumption rate being more seriously affected by glucose. Intracellularaccumulation of the reducing sugar from the mannose containingmedium proceeded much more rapidly and reached a higher levelthan with the glucose medium. However, trehalose accumulatedat a much higher rate with the glucose medium. Consequently,the net increase in cellular carbohydrates, as calculated fromthe amount of reducing sugar and trehalose, proceeded much morerapidly in the glucose medium. We concluded that the differencein the rates of utilization of glucose and mannose might bedue to the difference in the rates of uptake of both sugars. ¹Present adress: Department of Biology, Faculty of Science,Osaka City University, Sumiyoshiku, Osaka 558. To whom reprintrequests should be adressed. (Received June 24, 1975; )     

A Versatile Chromatographic Procedure for Purifying PS II Reaction Center Complex from Digitonin Extracts of Spinach Thylakoids

A versatile, two-step chromatographic method using DEAE-Toyopearl(Toyo Soda, Japan) is described for purifying photosystem IIreaction center complex from digitonin extracts of spinach thylakoidmembranes. The method is very simple and brings about an approximatefour-fold increase in the specific activity, on a chlorophyllbasis, of 2,4-dichlorophenol-indophenol photoreduction with1,5-diphenylcarbazide (to about 2,000 µ electron equivalentsper mg chlorophyll per h), with an approximate 40 percent recoveryin chlorophyll. The SDS-polyacrylamide gel electrophoresis performedin the presence of 4 M urea in the analyzing gel shows fourpolypeptide bands of the photosystem II reaction center of about47, 43, 30 and 9 kilodaltons. The absorption and fluorescence properties, as well as the pigmentand chemical compositions and the above mentioned polypeptideprofile of the purified complex are essentially identical withthose of the preparations isolated by the previously describedmethod (Satoh 1982). The digitonin solubilization of thylakoid membranes destroysthe water splitting machinery, so that the purified complexshows no oxygen evolving activity, even although 0.6–0.7atoms of manganese per 50 chlorophyll molecules still remain. (Received March 19, 1985; Accepted July 19, 1985)     

Incisor Abnormality of Senescence Accelerated Mouse (SAM)1

Incisor abnormalities such as loss of enamel color, hypoplasia of enamel, shortening and lengthening, irregular shape of edge, and fracture were often observed in SAM-P/2/Iw (senescence accelerated mouse-prone) more than 12 months old. On the other hand, for SAM-R/1/lw (control) mice more than 20 months old, there were only a few instances of loss of enamel color. The incidence of incisor abnormality was significantly different between P/2/Iw and R/I/Iw. The onset of abnormality was also earlier in P/2/Iw. Histologically, dens in dente and odontoma-like structures were occasionally found in the incisors of P/2/Iw. These findings add further supporting evidence that SAM-P/2/Iw is truly senescence accelerated.     

The fitting of the logistic equation to the rate of increase of population density

Though there are many problems on the usefulness of the logistic curve, it may be necessary to examine before discussing these problems whether or not the actual data fit to the theoretical values. It has been clarified in this paper that the relation between the population density and its rate of increase per individual described by the differential equation (1) is represented by a straight line on a finite difference diagram on which N_i+1−N_i/N_i values are plotted against N_i+1. Utilizing this linear relation we may examine the fittness of the logistic curve to the actual data and when it is fitted we may estimate the parameters of the logistic equation by (5) and (6). The result of the application of this method to the experimental populations of azuki bean weevil indicates that the relation between parent and progeny densities fits well to the logistic type as has been proved byFujita andUtida (1953) who utilized the linear reltion between 1/R+2σ and parent density where R is the apparent rate of reproduction and σ is a constant dependent primarily upon the length of adult life (0≦σ≦1).     

Alkaline phosphatase isozymes in the midgut of silkworm: purification of high pH-stable microvillus and labile cytosolic enzymes

Summary Genetically defined alkaline phosphatase (ALP) isozymes from the larval midgut tissues ofBombyx mori were purified and characterized. The membrane-bound form (m-ALP) was solubilized with 1% Triton X-100, then purified by DEAE-Sephacel, Con A-Sepharose 4B and Ultrogel AcA 34 column chromatography. The soluble form (s-ALP) was purified by DEAE-Sephacel, epoxy Toyopearl coupled with phosphonic acid and Ultrogel AcA 34 column chromatography. About 840- and 650-fold purification were achieved for m-ALP and s-ALP, respectively, and both ALPs were homogeneous as judged by poly-acrylamide gel electrophoresis. Both forms were found to be similar (MW=68 000 in gel permeation chromatography, and a single subunit as a monomer in denaturing SDS-polyacrylamide gels with MW=58 000 for m-ALP and MW=61 000 for s-ALP). The pH optima of ALPs were shown to lie at 10.9 (m-ALP) and 9.8 (s-ALP), the former being extremely stable even in pH 10–12 which accords with the physiological milieu inBombyx midgut lumen. The K_m values of the m-ALP and s-ALP forp-nitrophenyl phosphate were 1.99 and 1.49 mM, respectively. Both ALPs had a similar substrate specificity.l-Cysteine strongly inhibited both ALPs, but inhibitory effects ofl-phenylalanine,l-homoarginine andl-leucine were undetectable for s-ALP and very weak for m-ALP. A comparison of enzymatic properties on two ALPs suggested that each isozyme plays different roles.Abbreviations m-ALP membrane-bound alkaline phosphatase - s-ALP soluble alkaline phosphatase