Packing forces in ribonuclease crystals

Packing in Ribonuclease A and Ribonuclease S crystals have been compared in order to determine the possible role of the precipitant on lattice contacts. Both proteins have similar tertiary structures, but they crystallize in different space groups depending on the precipitating agent. It is found that packing differs either by the number of nearest neighbours or by the size of surface areas buried in individual contacts. Ammonium sulfate seems to promote hydrophobic interactions with interfaces similar to those found in oligomeric proteins. Organic precipitants favour electrostatic interactions.     

Crystallization and preliminary x-ray diffraction study of the flavoprotein NADH peroxidase from Streptococcus faecalis 10C1

NADH peroxidase from Streptococcus faecalis 10C1 has been crystallized from ammonium sulfate solutions using the hanging drop vapor diffusion method. Depending on pH, the crystals grew in the orthorhombic space group I222 or one of its subgroups P222 or P2(1)2(1)2 (or one of its two permutations). In both cases the unit cell axes are a = 76.6 A, b = 132.9 A, and c = 145.7 A. There are two monomers/asymmetric unit in the body-centered crystal form and four in the primitive one. The enzyme is catalytically active in the crystalline state. The crystals diffract to at least 2.5 A resolution; they are stable in the x-ray beam and hence suitable for detailed three-dimensional structure determination.     

A decade of diabetes: keeping children out of hospital.

OBJECTIVES--To document the number of children aged less than 15 years who developed diabetes and were managed within one large health district, and to evaluate the outcome of those children managed without hospital admission at diagnosis. DESIGN--A retrospective study over 1979-88, when a paediatrician and a physician with special interests in childhood diabetes initiated joint clinics. Data collected from the district diabetes register and files of consultants and health visitors specialising in diabetes. SETTING--Referral of children to consultants in Leicestershire (total population 863,000). MAIN OUTCOME MEASURES--The proportion of children managed without hospital admission, comparison of readmission rates and glycated haemoglobin concentrations between children admitted and those not admitted. RESULTS--Over 10 years 236 children aged 10-14 years developed diabetes (annual incidence rate 12.8/100,000 child population (95% confidence interval 11.3 to 14.7)). In total 138 were not admitted to hospital but received supervised management based at home. Admitted children were younger or acidotic or their family doctors did not contact the diabetes team. Duration of admission declined from seven days in 1979-80 to three days in 1987-8. Ninety two were not admitted to hospital during the 10 years for any reason. Significantly fewer children who received management at home were readmitted for reasons related to diabetes than the group treated in hospital (30 (22%) v 40 (41%); p = 0.004). Concentrations of glycated haemoglobin were no different between the two groups. CONCLUSIONS--Children with newly diagnosed diabetes may be safely and effectively managed out of hospital. Domiciliary or community based management depends on the commitment of consultants specialising in diabetes working in close cooperation with general practitioners, specialist nurses in diabetes, and dietitians.     

Assessment of cell proliferation on porous microcarriers by means of image analysis

Spherical porous microcarriers (PMCs) made from collagen-glycosaminoglycan crosslinked copolymers have exhibited considerable promise as growth surfaces for the proliferation of anchorage-dependent mammalian cell lines and have demonstrated the ability to entrap anchorage-independent cells. However, quantification of cell growth on PMCs has proved difficult. A method of measuring the proliferation of PMCs, based on image analysis, is presented. Using CV1 and CHO cell lines, samples of PMCs were removed from culture at various times, fixed, embedded and sectioned. The 2 microns sections were stained, photographed and digitized in three colors. A computer program was developed to evaluate digitized PMC cross-sections and to classify pixels as conforming to either background, cytoplasmic, matrix or nuclear parameters, based on a set of classification rules determined by statistical analysis. Growth curves were generated by relating the number of pixels occupied by cellular material to the total number of pixels in the PMC cross-section. The PMCs were found to foster cell proliferation, with cell densities approaching 100% occupancy.     

A multiple chemostat system for consortia studies on microbially influenced corrosion

A multiple chemostat system has been developed in which metal specimens can be exposed to a consortium of bacteria. The system comprises a single test chemostat containing the test specimen operated at a high dilution rate to facilitate the wash out of planktonic bacteria, selecting for attached or biofilm growth. This chemostat is fed at a steady low rate by a number of separate chemostats each of which contains a pure axenic culture of one member of the consortium being tested. This system has the advantage of providing a continual inoculum of the test species to the test specimen allowing both aerobic and anaerobic bacteria to be grown in the same system. Constant levels of three bacterial types were maintained in the system: Pseudomonas aeruginosa, Thiobacillus ferrooxidans and Desulfovibrio vulgaris. Exposure of 316L stainless steel electrodes to this system resulted in increased corrosion of coupons exposed biotically, as compared to those exposed abiotically. A current monitoring technique and electrochemical impedance spectroscopy were used to evaluate effects of bacteria on metallic corrosion.     

Selective staining of nucleic acids by osmium-ammine complex in thin sections from lowicryl-embedded samples

Osmium-ammine (OA)/SO2 selectively contrasted RNA- and DNA-containing structures in thin sections from Lowicryl-embedded samples. No cell structures were stained after Epon embedding. RNAse and DNAse digestion experiments demonstrated that only RNA and DNA were stained in Lowicryl thin sections. Protease digestion did not modify the staining reaction. The very fine end-reaction produced a very high resolution of the stained structures. The staining reaction was not due to the presence of SO2 but to the low pH of the solution (ranging from 1.5-2.2). OA in glycine buffer, pH 1.5, selectively contrasted nucleic acids. Electrostatic bonds between nucleic acids and OA complex were probably involved in the staining reaction. Increasing the pH value of the staining medium resulted in loss of OA specificity for nucleic acids. The high electrolyte concentration of the staining medium hindered the staining reaction.