Decomposition of cellulose in soils

1. Cellulose decomposition in forest and orchard soils was investigated by studying the breakdown of boiled and washed cellophane in the soils and in vitro. Decomposition occurred from quick to slow in the order: orchard on clay soil, forest on clay soil, forest on sandy loam, and in the latter in the order: calcareous mull, acid mull and mor. 2. In the different forest soils which were investigated the rate of decomposition was parallel to their water capacity. It slowed down considerably when the water content of the soil decreased, especially after the wilting point was reached. 3. Of the fungi isolated from these soils, those from orchard soil — 5% to 50%Fusarium spp. — were among the fastest decomposers of cellulose. This agrees with, and may explain the high rate of decomposition in orchard soil. 4. Decomposition in pure culture is quicker than in soil. As filtersterilized soil extract checked the decomposition in pure culture, but heat-sterilized soil extract did not, an extractable but heat-sensitive substance may be one retarding factor.     

On the formation of adipocere from fats

Summary The formation of adipocere is a process occurring under virtually anaerobic conditions in which human fat is converted into a complex of saturated fatty acids by a great variety of bacterial species occurring in and on the decomposing body.     

Evolution of eye lens crystallins: the stress connection

Crystallins, the structural proteins of the eye lens, ensure the transparency and integrity of the lens throughout life. Recent sequence comparisons have shown that evolution has recruited crystallins among already existing heat-shock proteins and stress-inducible enzymes.     

Inositol 1,4,5-trisphosphate-induced calcium release in the organelle layers of the stratified, intact egg of Xenopus laevis

Using double-barreled, Ca2(+)-sensitive microelectrodes, we have examined the characteristics of the Ca2+ release by inositol 1,4,5-trisphosphate (Ins(1,4,5)P3) in the various layers of Xenopus laevis eggs in which the organelles had been stratified by centrifugation. Centrifugation of living eggs stratifies the organelles yet retains them in the normal cytoplasmic milieu. The local increase in intracellular free Ca2+ in each layer was directly measured under physiological conditions using theta-tubing, double-barreled, Ca2(+)-sensitive microelectrodes in which one barrel was filled with the Ca2+ sensor and the other was filled with Ins(1,4,5)P3 for microinjection. The two tips of these electrodes were very close to each other (3 microns apart) enabling us to measure the kinetics of both the highly localized intracellular Ca2+ release and its subsequent removal in response to Ins(1,4,5)P3 injection. Upon Ins(1,4,5)P3 injection, the ER-enriched layer exhibited the largest release of Ca2+ in a dosage-dependent manner, whereas the other layers, mitochondria, lipid, and yolk, released 10-fold less Ca2+ in a dosage-independent manner. The removal of released Ca2+ took place within approximately 1 min. The sensitivity to Ins(1,4,5)P3 and the time course of intracellular Ca2+ release in the unstratified (unactivated) egg is nearly identical to that observed in the ER layer of the stratified egg. Our data suggest that the ER is the major organelle of the Ins(1,4,5)P3-sensitive Ca2+ store in the egg of Xenopus laevis.     

Purification of the microsomal Ca2+-ATPase from rat liver

Summary The Ca²⁺-ATPase from rat liver microsomes has been solubilized in Triton X-100 and purified to homogeneity by ficollsucrose treatment, column chromatography with agarose-hexane adenosine 5-triphosphate Type 2, and high pressure liquid chromatography (HPLC). The purified enzyme obtained by this sequential procedure exhibited a 183-fold increase in specific activity. After ficoll-sucrose treatment, the activity of the Ca²⁺-ATPase was stable for at least two weeks when stored at –70°C. In SDS-polyacrylamide gels, several fractions from HPLC chromatography showed a single band at a position corresponding to a molecular weight of about 107 kDa. This value is consistent with the molecular weight of the phosphoenzyme intermediate of endoplasmic reticulum (ER) Ca²⁺-ATPase. Further characterization of the ER Ca²⁺-ATPase was performed by western immunoblots. Antiserum raised against the 100-kDa sarcoplasmic reticulum (SR) Ca²⁺-ATPase cross-reacted with the purified Ca²⁺-ATPase from rat liver ER membranes.     

Extreme differences in charge changes during protein evolution

Summary The maintenance of a proper distribution of charged amino acid residues might be expected to be an important factor in protein evolution. We therefore compared the inferred changes in charge during the evolution of 43 protein families with the changes expected on the basis of random base substitutions. It was found that certain proteins, like the eye lens crystallins and most histones, display an extreme avoidance of changes in charge. Other proteins, like phospholipase A2 and ferredoxin, apparently have sustained more charged replacements than expected, suggesting a positive selection for changes in charge. Depending on function and structure of a protein, charged residues apparently can be important targets for selective forces in protein evolution. It appears that actual biased codon usage tends to decrease the proportion of charged amino acid replacements. The influence of nonrandomness of mutations is more equivocal. Genes that use the mitochondrial instead of the universal code lower the probability that charge changes will occur in the encoded proteins.     

Short-term stimulatory effect of Sertoli cell conditioned medium on Leydig cell steroidogenesis is not mediated by inhibin

Addition of concentrated rat Sertoli cell conditioned medium (rSCCM) to isolated Leydig cells from immature rats stimulated steroid production more than 13-fold within 4 h. LH-stimulated steroidogenesis was not enhanced by addition of rSCCM. The biological activity of the concentrated rSCCM was higher after incubation of Sertoli cells with FSH, whereas FSH alone did not stimulate steroid production. This effect of rSCCM was not due to inhibin, since highly purified 32 kDa rat inhibin, in doses equivalent to those present in rSCCM, had no effect on steroidogenesis during the 4 h incubation period. Furthermore, inhibin could be separated from the Leydig cell stimulating factor by anion-exchange chromatography. These results indicate a short-term paracrine control of Leydig cell steroidogenesis by Sertoli cell derived factors, which differ from inhibin.     

大肠杆菌青霉素G酰化酶基因及其邻近区域的核苷酸全序列

Some of microorganisms have been known to possess penicillin G acylase activity. The E. coli derived penicillin G acylase (PGA) can catalyze the conversion of penicillin G into phenylacetic acid and 6-amino-penicillanic acid, the latter is used as the starting compound for the industrial formation of semi-synthetic penicillins. Apart from its industrial importance, the enzyme PGA displays a number of interesting properties. Catalytically active enzyme is localized in the periplasmic space of E. coli cells and composed of two dissimilar subunits. The two subunits are apparently produced from a precursor protein, via a processing pathway hitherto unique in its features for a prokaryotic enzyme. The studies on processing of the precursor and on the relationship between structure and function of the mature enzyme are important theoretically. Previously we cloned a 3.5 kb DNA fragment from a strain (E. coli AS 1.76), which displays PGA activity. In this paper, we report a nucleotide sequence of the 3.5 kb DNA fragment containing PGA gene. After insertion of the DNA fragment into EcoR I and Hind III sites in pWR 13, pPGA 20 had been obtained. We subcloned the Hind III and Bg1 II treated fragment of 1.6 kb in length from pPGA 20 into Hind III and BamH I sites of pWR 13 to get a pPGA 1.6, and Bg1 II and EcoR I treated fragment of 1.9 kb in length into BamH I and EcoR I sites of pWR 13 to get a pPGA 1.9. The linearized pPGA 1.9 which were digested with appropriate restriction enzymes were progressively shortened from both ends respectively by digestion with Bal 31 nuclease, followed by cleavage of shortened target DNA off vector DNA molecules with appropriate restriction enzymes. The series of the DNA fragments shortened from EcoR I end were then cloned into plasmid pWR 13 which had previously digested with Hind III and Sma I enzymes (Fig. 1). The DNA fragment cloned in pWR 13 were directly sequenced on the resulted plasmids by using primer I and primer II. Thus we have obtained the complete nucleotide sequence of the 3.5 kb DNA fragment. The 3.5 kb fragment contains an intact PGA gene which is 2.6 kb.(ABSTRACT TRUNCATED AT 400 WORDS)     

A neural network algorithm for the multiple traveling salesmen problem

We developed an efficient neural network algorithm for solving the Multiple Traveling Salesmen Problem (MTSP). A new transformation of the N-city M-salesmen MTSP to the standard Traveling Salesmen Problem (TSP) is introduced. The transformed problem is represented by an expanded version of Hopfield-Tank's neuromorphic city-position map with (N + M-1)-cities and a single fictitious salesmen. The dynamic model associated with the problem is based on the Basic Differential Multiplier Method (BDMM) [26] which evaluates Lagrange multipliers simultaneously with the problem's state variables. The algorithm was successfully tested on many problems with up to 30 cities and five salesmen. In all test cases, the algorithm always converged to valid solutions. The great advantage of this kind of algorithm is that it can provide solutions to complex decision making problems directly by solving a system of ordinary differential equations. No learning steps, logical if statements or adjusting of parameters are required during the computation. The algorithm can therefore be implemented in hardware to solve complex constraint satisfaction problems such as the MTSP at the speed of analog silicon VLSI devices or possibly future optical neural computers.