Optically detected magnetic resonance studies of porcine pancreatic phospholipase A2 binding to a negatively charged substrate analogue

The direct binding of porcine pancreatic phospholipase A2 and its zymogen to 1,2-bis(heptanylcarbamoyl)-rac-glycerol 3-sulfate was studied by optical detection of triplet-state magnetic resonance spectroscopy in zero applied magnetic field. The zero-field splittings of the single Trp3 residue undergo significant changes upon binding of phospholipase A2 to lipid. Shifts in zero-field splittings, characterized mainly by a reduction of the E parameter from 1.215 to 1.144 GHz, point to large changes in the Trp3 local environment which accompany the complexing of phospholipase A2 with lipid. This may be attributed to Stark effects caused by the binding of a charged group near Trp3 in the enzyme-lipid complex. The cofactor, Ca2+, which is strongly bound to the enzyme active site, has an influence on the bonding, as reflected by smaller zero-field splitting shifts. A relatively small change in the Trp environment was observed for the interaction of the zymogen with lipid.     

Human lymphocyte tubulin: Purification and characterization in normal and leukemic cells

Tubulin has been purified from human blood and tonsil lymphocytes. Using gel filtration, the molecular weight of human lymphocyte tubulin was estimated to be 119 000. The proteins was shown to consist of two subunits, with molecular weights of 61 000 and 58 000 comparable to the α and β polypeptides of human brain tubulin. A partial identity reaction was observed between lymphocyte tubulin and human tubulin when tested by double immunodiffusion against a rabbit anti-human brain tubulin antibody. In the presence of GTP, the purified protein polymerized to form microtubules. Tubulin was localized to the cell's juxtacentriolar region by immunofluorescence and electron microscopy. When assayed by a colchicine-binding assay corrected for time decay, the binding affinity was 1.50 ± 0.86 · 10⁶M^?1 and a level in normal lymphocytes of 1.21 · 10^?2 ± 0.79 g/g of soluble protein was determined. Since chronic lymphocytic leukemia lymphocytes have an anomalous capping behavior as well as an unusual susceptibility to colchicine toxicity, the properties and levels of tubulin were determined in these cells. Similar values were obtained for the level, decay rate, molecular weight, and K_a for colchicine as for normal lymphocytes. Chronic lymphocytic leukemia lymphocyte tubulin polymerized in a normal fashion. It thus appears that a decrease in the quantity or function of tubulin does not account for these anomalies in the chronic lymphocytic leukemia lymphocyte.     

Vegetativ vermehrbare Birnenunterlagen

Theoretical and Applied Genetics -     

The light-harvesting and protective functions of carotenoids in photosynthetic membranes

Siefermann-Harms, D. 1987. The light-harvesting and protective functions of carotenoids in photosynthetic membranes.     

Variation in early neonatal mortality for different types of fetal growth retardation

Birth and first-48-hr death records were analyzed for 10,024 liveborn infants in Mexico City and 12,786 liveborn infants in Santa Cruz, Bolivia. The objective of the analysis was to characterize the early postnatal mortality rates for different types of fetal growth retardation and prematurity. Infants who were delivered prior to 37 weeks of gestation had 23-100 times the mortality risk of infants born at full term and normal weight. Light-for-gestational-age infants (birth weight less than 2,900 g) were further divided into proportionately growth-retarded with normal Rohrer's index (weight/height) and disproportionately growth-retarded with low Rohrer's index. The proportionately growth-retarded infant had nearly twice the mortality of the full-term, appropriate-weight infants, whereas the disproportionately growth-retarded infants had 2.9-5.7 times the mortality rate of the full-term, appropriate-weight infants. There were some differences between samples in mortality rates and prevalence of the different classes of small infants, but the pattern of mortality within samples was consistent between samples.     

Molecular dynamics of the alpha-helical epitope of a novel synthetic lipopeptide foot-and-mouth disease virus vaccine

A novel synthetic foot-and-mouth disease virus (FMDV) peptide vaccine consisting of a synthetic B-cell and macrophage activator covalently linked to an amphiphilic alpha-helical T-cell epitope was developed. The low molecular weight vaccine of 3400 daltons is composed of virus VP1 antigenic determinant and the immunologically active lipotripeptide tripalmitoyl-S-glyceryl-cysteinyl-seryl-serine (P3CSS) as built-in adjuvant. The vaccine, tripalmitoyl-S-glyceryl-cysteinyl-seryl-seryl-FMDV-VP1 (VP1 = serotype O1K 135-154) induces protection against homologous challenge and serotype-specific virus neutralizing antibodies in guinea pigs after single administration without further adjuvants or carriers. A P3CSS conjugate with the FMDV-VP1 segment 135-154 of strain O Wuppertal produced only poor cross-protection against challenge with O1K virus. The antigenic determinant VP1(135-154) is an amphiphilic alpha-helix, as shown by CD. Molecular dynamics simulations (MDS) carried out using the highly homologous alpha-helical alcohol dehydrogenase (ADH) segment H3 as starting conformation for VP1(138-149) suggest that the FMDV segment 138-149 may adopt alpha-helical conformation during binding to its T-cell receptor, and that the development of the system during MDS may be considered as the dissociation step of the complex.     

Estimation of microbial densities from dilution count experiments.

Although dilution counts have been widely used in quantitative microbiology, their interpretation has always been widely discussed both in microbiology and in applied statistics. Maximum-likelihood (most-probable-number) methods hae generally been used to estimate densities from dilution experiments. It has not been widely recognized that these methods are intrinsically and statistically biased at the sample sizes used in microbiology. This paper presents an analysis of proposed method for correction of such biases, and the method was found to be robust for moderate deviations from Poisson behavior. For analyses at greater variance with the Poisson assumptions, the use of the Spearman-Karber method is analyzed and shown to yield an estimate of density of lesser bias than that produced by the most-probable-number method. Revised methods of constructing confidence limits proposed by Loyer and Hamilton (M.W. Loyer and M.A. Hamilton, Biometrics 40:907-916, 1984) are also discussed, and charts for the three- and four-decimal dilution series with five tubes per dilution are presented.     

Superoxide dismutase amplifies dye photosensitized production of desferal free radical: an electron spin resonance study

Desferal free radical (DFFR) photogenerated from dye sensitization was studied by electron spin resonance. When irradiated at the visible maximum in the presence of O2, both rose bengal and riboflavin sensitized the oxidation of Desferal (DF) and generated the DFFR. The yield of DFFR was amplified by superoxide dismutase (SOD). The SOD enhancement was attributed to the inhibition of superoxide-induced DFFR destruction. Similar SOD enhancement was observed with dyes Rhodamine 123 and Gentian Violet. Our studies suggest that when Desferal is used as a chelating agent in the presence of SOD, systems involving O2- could face interference from DFFR even at concentrations as low as 10 microM DF. DFFR may interfere with the chain reaction of lipid peroxidation resulting in an apparent protective action which, in fact, has very little to do with chelating the catalytic iron.