Characteristics of 2-oxoglutarate and glutamate transport in spinach chloroplasts

The transport of glutamate, 2-oxoglutarate and malate in intact spinach chloroplasts was determined using a double-silicone-layer centrifugation technique in which the silicone layers stayed separated at the end of centrifugation. Glutamate was found to be transported via the dicarboxylate but not the 2-oxoglutarate translocator. Hence the kinetic parameters (i.e.K _m,K _i andV _max) determined in glutamate-preloaded chloroplasts represent the kinetic constants of the dicarboxylate translocator. Measurements from malate- or succinate-preloaded chloroplasts represent the aggregate values of both the dicarboxylate and the 2-oxoglutarate translocators. Calculations showed that the 2-oxoglutarate and glutamate transport required to support the high fluxes of photorespiratory NH₃ recycling could be achieved if the transport of these two dicarboxylates occurred on separate translocators. It is proposed that during photorespiration the transport of 2-oxoglutarate into and glutamate out of the chloroplast occurred via the 2-oxoglutarate and the dicarboxylate translocators, respectively. These transports are coupled to malate counter-exchange in a cascade-like manner resulting in a net 2-oxoglutarate/glutamate exchange with no net malate uptake.Abbreviation 2-OG 2-oxoglutarate     

Formation of wheat protein bodies: Involvement of the Golgi apparatus in gliadin transport

Developing wheat (Triticum aestivum L.) endosperm was examined using ultrathin sections prepared from tissues harvested at 5, 9, 16 and 25 d after flowering. Protein bodies were evident by 9 d and displayed a variety of membranous structures and inclusions. The Golgi apparatus was a prominent organelle at all stages, and by 9 d was associated with small electron-dense inclusions. By immunocytochemical techniques, gliadin (wheat prolamine) was localized within these vesicles and in homogeneous regions of protein bodies, but not in the lumen of the rough endoplasmic reticulum. The protein bodies appear to enlarge by fusion of smaller protein bodies resulting in larger, irregular-shaped organelles. The affinity of the Golgi-derived vesicles for gliadin-specific probes during the period of maximal storage-protein synthesis and deposition indicates that this organelle includes the bulk, if not all, of the gliadin produced. The involvement of the Golgi apparatus in the packaging of gliadins into protein bodies indicates a pathway which differs from the mode of prolamine deposition in other cereals such as maize, rice and sorghum, and resembles the mechanism employed for the storage of rice glutelin and legume globulins.Abbreviations ER endoplasmic reticulum - IgG immunoglobulin G - DAF days after flowering     

Collagen autoimmunity and arthritis

Collagen-induced arthritis in animals is an example of polyarthritis that sufficiently resembles human rheumatoid arthritis to be used as a model. It is caused by immunizing susceptible animals with type II collagen isolated from articular cartilage. Susceptibility is genetically determined and linked to the major histocompatibility locus. It is important because some human arthritis is also associated with major histocompatibility genes and may be caused or aggravated by the presence of autoimmunity to normal cartilage components. Collagen-induced arthritis is also important because it is an example of immunologically mediated joint destruction, which may share some of the mechanisms present in human disease. Although it is caused by autoimmunity to collagen, susceptibility and responsiveness to type II collagen are not completely correlated, and there are examples of animals with high levels of collagen immunity who do not develop arthritis. The initial lesion appears to be the deposition of an antibody on the surface of articular cartilage, which precedes development of overt arthritis by several days. Disease can be readily transferred with specific antibody. Arthritogenic antibodies appear to have restricted epitope specificity, which may partially explain the disparities between responsiveness to immunization with collagen and susceptibility to arthritis, but precise delineation of the epitopes involved has not yet been accomplished. Complement activation also appears to be intimately involved since the disease correlates with the presence of high levels of complement-binding IgG isotypes, and passive transfer is possible only into complement-sufficient recipients. Inflammation progresses rapidly so that cartilage destruction and marginal erosion develop over a period of a few days. Collagen-induced arthritis offers a unique opportunity to study autoimmune-mediated arthritis in which the inducing antigen is well characterized and readily available. Analysis of the disease has permitted the proposal of a schema for its pathogenesis.     

Enhancement of epidermal growth factor receptor expression on glioma cells by recombinant tumor necrosis factor α

Summary Recombinant tumor necrosis factor (rTNF; optimal dose 1000 U/ml) significantly increased the density of epidermal growth factor receptor (EGF-R) in three of four glioma cell lines in culture as determined by binding analysis of anti-EGF-R monoclonal antibody (mAb) 425. Since enhancement of EGF-R expression by rTNF- was inhibited when cells were treated with the protein synthesis inhibitor cycloheximide, the effects of rTNF may be protein-synthesis-dependent. The dose of rTNF that was optimal for up-regulation of EGF-R on glioma cells did not inhibit the growth of these cells.¹²⁵I-labeled mAb 425 lysed glioma cells in culture following its internalization into the cells. After glioma cells had been treated with rTNF, the growth-inhibitory effects of the mAb were significantly enhanced, probably a reflection of the increase in EGF-R density on the tumor cell surfaces. The rTNF effects were specific to the EGF-R and did not affect unrelated glioma-associated antigens. In our previous clinical trials,¹²⁵I-labeled mAb 425 showed immunotherapeutic effects in glioma patients. The present study provides the basis for considerations of combined immunotherapy of glioma patients with¹²⁵I-labeled mAb 425 and rTNF.     

Identification of three novel missense PKU mutations among Chinese.

Three novel missense mutations have been identified in the phenylalanine hydroxylase (PAH) genes of Chinese individuals afflicted with various degrees of phenylketonuria (PKU). A T-to-C transition was observed in exon 5 of the gene, resulting in the substitution of Phe161 by Ser161. Two substitutions, G-to-T and T-to-G, were observed in exon 7, resulting in the substitution of Gly247 by Val247 and Leu255 by Val255, respectively. Expression analysis demonstrated that these mutant proteins produced between 0 and 15% of normal PAH enzyme activity. Population screening of a Chinese sample population indicates that these mutations are quite rare, together accounting for only about 4% of all PKU alleles among the Chinese. The P161S and G247V mutations were each present on a single PAH RFLP haplotype 4 chromosome in patients form Northern China, while the L255V mutation was present on chromosomes of both haplotypes 18 and 21 in patients from Southern China. These results suggest that the remaining 30% of uncharacterized PKU alleles in the Chinese population may bear a large number of relatively rare PAH mutations.     

In vitro effects of fetal bovine serum and glucose on multiplication of Cryptobia salmositica

Cryptobia salmositica multiplied rapidly at 10 C in a minimum essential medium (containing 1.0 mg glucose/ml, Hanks' salts and L-glutamine) supplemented with heat-inactivated fetal bovine serum (FBS) and HEPES buffer (25 mM). The multiplication rate of C. salmositica was related to the amount of FBS; the peak number (approximately 9 x 10(6) parasites/ml) was attained in about 6 wk when the medium contained 25% final concentration of FBS. Glucose utilization was related to the number of parasites; the maximum utilization was reached before peak numbers. Formation of rosette colonies was correlated with multiplication rate and numbers of parasites in cultures. Degenerate round forms found in old cultures probably were caused by the accumulation of metabolic wastes in the medium.     

Metacercarial infections of Paragonimus westermani in freshwater crabs sold in markets in Seoul

Status of metacercarial infections of Paragonimus westermani was observed in freshwater crabs, which were purchased at 3 markets in its peak season of 1990. All of 85 crabs were Eriocheir japonicus. No other species of Eriocheir were found. When crushed muscle and viscera was examined individually, the infection rate was 11.8%; and mean number of metacercariae was 2.1 per infected crab. Unless adequately cooked, freshwater crabs are still potential sources of human paragonimiasis.     

Component proteins in crude extract of adult Paragonimus westermani purified by immunoaffinity chromatography using monoclonal antibodies.

The nature of 2 component proteins in crude saline extract of adult Paragonimus westermani was investigated. By immunoaffinity chromatography using monoclonal antibodies (MAb) as ligands, the proteins were purified from the crude extract. Band 1 protein in disc-polyacrylamide gel electrophoresis (PAGE) was purified by PFCK-136 MAb. The protein, known to have molecular mass of 440 kDa, was composed of 23, 46 and 92 kDa subunits when observed by reducing SDS-PAGE and SDS-PAGE/immunoblot. This protein was originated from eggs of the worm as revealed by immunohistochemical staining with PFCK-136 Mab. Another affinity purified protein utilizing PFCK-44 MAb was the band 4 protein of 17 kDa in disc-PAGE. This was a monomer protein in reducing SDS-PAGE and SDS-PAGE/immunoblot. The protein was produced at intestinal epithelium of the worm.     

Application of a stability statistic to international maize yield trials

Summary Genotype x environment (GE) interaction encountered in experiments complicates genotype selection and varietal recommendation. The integration of yield and stability of genotypes into a single parameter may make selection and recommendation easier. Kang developed a rank-sum method that allows selection for both yield and the stability variance statistics ( _i ² or s _i ² ) of Shukla. The objective of this research was to compare the rank-sum selection method to selection based on yield alone in five international maize (Zea mays L.) yield trials. Ranks were assigned for yield (the highest mean yield received a rank of 1) and for _i ² and s _i ² (the lowest value received a rank of 1). The yield and _i ² ranks and/or the yield and s _i ² ranks for each genotype were summed. Each trial contained two reference entries (REs). Yield rank or rank-sum of each genotype was compared to yield rank or rank-sum of the best RE (BRE). GE interaction was significant for all trials. Heterogeneity in the GE interaction due to the linear effect of a covariate (differences in fertility and/or cultural practices) was significant in Trials 1, 2, and 5. Overall, in all trials, 29 genotypes were selected on the basis of yield alone. On the basis of _i ² and yield rank-sum, 32 genotypes were identified, with 11 being lower yielding than the 29 yield-based selections. On the basis of s _i ² and yield rank-sum, 31 genotypes were selected, with 11 being lower yielding than the yield-bases selections. Obviously, yield is sacrificed when the rank-sum method is used in the selection process. However, selection based on yield alone may not be adequate when GE interaction is significant because of testing in diverse environments.