Aldolase and actin protect rabbit muscle lactate dehydrogenase from ascorbate inhibition

Muscle-type LDH (LDH-m4) activity is critical for efficient anaerobic glycolysis. The results here show that rabbit LDH-M4 is inhibited by concentrations of ascorbate normally found in tissues. Aldolase and muscle G-actin were found to protect and to reverse inhibitions of LDH-m4 by ascorbate. G-actins showed some species specificity. Myosin, tropomyosin and troponin from rabbit muscle and muscle proteins from other animal sources had no affect on the inhibitions by ascorbate. The substrate inhibition of LDH-m4 by pyruvate is partially relieved by the presence of aldolase and lowers the Km without affecting the Vm. G-actin under similar conditions has no affect. It is believed that these studies reflect some of the resting properties of glycolytic enzymes that bind and unbind to contractile elements. It is proposed that ascorbate facilitates the storage of glycogen in muscle at rest by inhibiting glycolysis.     

Functional stabilization of trypsin by conjugation with beta-cyclodextrin-modified carboxymethylcellulose

Bovine pancreatic trypsin was chemically modified by a beta-cyclodextrin-carboxymethylcellulose polymer using 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide as coupling agent. The conjugate retained 110% and 95% of the initial esterolytic and proteolytic activity, respectively, and contained about 2 mol of polymer per mol of trypsin. The optimum temperature for trypsin was increased to 8 degrees C after conjugation. The thermostability of the enzyme was increased to about 16 degrees C after modification. The conjugate prepared was also more stable against thermal incubation at different temperatures ranging from 45 degrees C to 60 degrees C. In comparison with native trypsin, the polymer-enzyme complex was more resistant to autolytic degradation at pH 9.0, retaining about 65% of the initial activity after 3h incubation. In addition, modification protected trypsin against denaturation in the presence of sodium dodecylsulfate.     

Lack of correlation between seminal and plasma HIV-1 viral loads is associated with CD4 T cell depletion in therapy-naïve HIV-1+ patients

The present study was conducted to investigate a possible correlation between plasma (PVL) and seminal viral load (SVL) on treatment-na?ve HIV-1-infected patients in Vitória, ES, Brazil. We also evaluated whether the progressive immunosuppression associated with HIV disease (as evidenced by declining CD4 T cell counts) has any impact on the correlation between PVL and SVL HIV-1. Viral load on paired blood and semen samples from 56 consecutive treatment-na?ve patients were evaluated and compared to CD4 cell counts. Viral load and T cell counts (cells/microl) were determined by NASBA and by flow cytometry, respectively. Overall, a strong positive correlation between PVL and SVL (rho = 0.438, p = 0.001) was observed. However, when patients were grouped according to their CD4 counts, this correlation was only significant among patients with CD4 counts > 200 cells/microl. Results presented here demonstrate the existence of a strong correlation between PVL and SVL on patients with CD4 cell counts > 200 cells/microl, suggesting that this association may correlate with disease progression.     

Towards a bioinformatics network for Latin America and the Caribbean (LACBioNet)

Bioinformatics is increasingly recognised as a crucial field for research and development in the biological sciences, and forms an integral part of genomics, proteomics and modern biotechnology. Worldwide participation is important, and scientists in developing countries can contribute to this field. Regional networks for bioinformatics are highly beneficial for capacity strengthening and cooperation, and for establishing productive interactions between scientists in the fields of biological and informatics sciences. Such a network (LACBioNet) is being organised for Latin America and the Caribbean. Its immediate goals include the organisation and extension of nodes and services, information and communication, research and development in different specialty fields of bioinformatics, and training and human resource development.     

Functional stabilization of invertase by covalent modification with pectin

Pectin was attached to ethylenediamine-activated carbohydrate moieties of invertase using 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide as coupling agent. The modified enzyme retained 57% of the original activity and contained 2.7 mol polymer per mol holoenzyme. Its optimum temperature was increased by 8°C and its thermostability by 7.3°C. The half-life at 65°C was increased from 5 min to 2 days. The enzyme stability was enhanced by 33% at pH 2.0, and also by 27% at pH 12.0. The conjugate retained about 96% of its initial activity after 3 h incubation in 6 M urea.     

Increased Conformational and Thermal Stability Properties for Phenylalanine Dehydrogenase by Chemical Glycosidation with End-group Activated Dextran

A mono-aminated dextran derivative was attached to Bacillus badius phenylalanine dehydrogenase via a carbodiimide-catalyzed reaction. The optimum temperature for the conjugate was 10 °C higher than for native enzyme, and its thermostability was improved by 8 °C. The activation free energy of thermal inactivation at 45 °C was increased by 16.8 kJ/mol. The improved conformational stability of the modified enzyme was confirmed by fluorescence spectroscopy.     

Influences of land use and stream size on particulate and dissolved materials in a small Amazonian stream network

We investigated the influences of forest or pasture land use and stream size on particulate and dissolved material concentrations in a network of second to third order streams in Rondônia, in the Brazilian Amazon. During the dry season, a second order stream originating in pasture had lower concentrations of dissolved oxygen and nitrate, higher concentrations of chlorophyll, total suspended solids, particulate organic carbon, particular organic nitrogen, ammonium, and phosphate than a second order stream originating in forest. Where the second order forest stream exited forest and entered pasture, concentrations of dissolved oxygen dropped from 6 mg/L to almost 0 mg/L and nitrate concentrations dropped from 12 M to 2 M over a reach of 2 km. These changes indicated a strong influence of land use. During the rainy season, differences among reaches of all particulate and dissolved materials were diminished. Concentrations of oxygen, chlorophyll, total suspended solids, particulate organic carbon and nitrogen, nitrate, ammonium, and phosphate in the third order pasture stream more closely resembled the second order forest stream than the second order pasture stream, suggesting that conditions in the channels of larger pasture streams more strongly control concentrations of these materials. If this pattern is widespread in stream networks of regions that consist of a mosaic of forest and pasture lands, it may have important consequences for understanding the effects of deforestation on larger rivers of the Amazon Basin. This would indicate that the effects of forest clearing on the concentrations of many suspended and dissolved materials will be most easily detected in very small streams but potentially difficult to detect in larger streams and rivers.     

Root distribution in an Amazonian seasonal forest as derived from δ13C profiles

Carbon isotope ratios of the main stem in trees, saplings, and seedlings were correlated with their main stem diameter in an Amazonian seasonal forest. This correlation became the basis of using carbon isotope ratios of roots from various levels of the soil profile in order to determine root distribution from emergent, canopy and subcanopy trees, saplings and herbaceous understorey plants. It was observed that the distribution of roots in the soil profile is horizontally and vertically heterogeneous. Pockets of roots from saplings or herbaceous understorey plants were found as deep as 4 m and pockets of roots from emergent trees were found as shallow as 1 m depth.     

Adolescent Pregnancy and Attained Height among Black South African Girls: Matched-Pair Prospective Study

Importance

The impact of adolescent pregnancy on offspring birth outcomes has been widely studied, but less is known about its impact on the growth of the young mother herself.

Objective

To determine the association between adolescent pregnancy and attained height.

Design

Prospective birth cohort study.

Setting

Cohort members followed from birth to age 20 y in Soweto, South Africa.

Participant

From among 840 Black females with sufficient data, we identified 54 matched pairs, in which a girl who became pregnant before the age of 17 years was matched with a girl who did not have a pregnancy by age 20 y. Pairs were matched on age at menarche and height-for-age z scores in the year before the case became pregnant (mean 15.0 y).

Main Outcome Measures

The two groups were compared with respect to attained height, measured at mean age 18.5 y.

Results

Mean age at conception was 15.9 years (range: 13.7 to 16.9 y). Mean height at matching was 159.4 cm in the adolescent pregnancy group and 159.3 cm in the comparison group (p = 0.3). Mean attained height was 160.4 cm in the adolescent pregnancy group and 160.3 cm in the comparison group (p = 0.7).

Conclusions

Among Black females in Soweto, South Africa, adolescent pregnancy was not associated with attained height.     

Contributions of C3 and C4 plants to higher trophic levels in an Amazonian savanna

We studied the energy flow from C₃ and C₄ plants to higher trophic levels in a central Amazonian savanna by comparing the carbon stable-isotope ratios of potential food plants to the isotope ratios of species of different consumer groups. All C₄ plants encountered in our study area were grasses and all C₃ plants were bushes, shrubs or vines. Differences in δ¹³C ratios among bushes (xˉ = −30.8, SD = 1.2), vines (xˉ = −30.7, SD = 0.46) and trees (xˉ = −29.7, SD = 1.5) were small. However the mean δ¹³C ratio of dicotyledonous plants (xˉ = −30.4, SD = 1.3) was much more negative than that of the most common grasses (xˉ = −13.4, SD = 0.27). The insect primary consumers had δ¹³C ratios which ranged from a mean of −29.5 (SD = 0.47) for the grasshopper Tropidacris collaris to a mean of −14.7 (SD = 0.56) for a termite (Nasutitermes sp.), a range similar to that of the vegetation. However, the common insectivorous and omnivorous vertebrates had intermediate values for δ¹³C, indicating that carbon from different autotrophic sources mixes rapidly as it moves up the food chain. Despite this mixing, the frogs and lizards generally had higher values of δ¹³C (xˉ = −21.7, SD = 1.6; xˉ = −21.9, SD = 1.8, respectively) than the birds (xˉ = −24.8, SD = 1.8) and the only species of mammal resident in the savanna (xˉ = −25.4), indicating that they are generally more dependent on, or more able to utilise, food chains based on C₄ grasses. Received: 7 May 1998 / Accepted: 30 November 1998