NADPH/NADP+ ratio: regulatory implications in yeast glyoxylic acid cycle

Summary The utilization by yeast of two carbon sources is carried out through the operation of the glyoxylic acid cycle. Kinetic data from the isocitrate transforming enzymes suggest that the flow of isocitrate through the glyoxylic acid cycle depends upon the inhibition of the isocitrate decarboxylating enzymes. Both isocitrate dehydrogenases are inhibited by a mixture of glyoxylate + oxaloacetate, but for the reasons described in the text we consider that this inhibition is of no physiological significance. On the other hand, we have found that NADPH is a competitive inhibitor of NADP-isocitrate dehydrogenase with respect to NADP⁺, with a K_I similar to its K_M. It also produces an additive effect on the NADH-produced inhibition of NAD-isocitrate dehydrogenase. We propose NADPH as the compound that channels the utilization of isocitrate into the glyoxylic acid cycle. This is supported by the finding of an increased NADPH/NADP⁺ ratio in acetate grown yeast with respect to glucose grown cells.     

Studies on the Endoplasmic Reticulum : IV. Its Form and Distribution during Mitosis in Cells of Onion Root Tip

Cells of onion and garlic root tips were examined under the electron and phase contrast microscopes after fixation in KMnO₄. Special attention was focused on the distribution and behavior of the endoplasmic reticulum (ER) during the several phases of mitosis. Slender profiles, recognized as sections through thin lamellar units of the ER (most prominent in KMnO₄-fixed material), are distributed more or less uniformly in the cytoplasm of interphase cells and show occasional continuity with the nuclear envelope. In late prophase the nuclear envelope breaks down and its remnants plus cytoplasmic elements of the ER, which are morphologically identical, surround the spindle in a zone from which mitochondria, etc., are excluded. During metaphase these ER elements persist and concentrate as two separate systems in the polar caps or zones of the spindle. At about this same time they begin to proliferate and to invade the ends of the spindle. The invading lamellar units form drape-like partitions between the anaphase chromosomes. In late anaphase, their advancing margins reach the middle zone of the spindle and begin to fray out. Finally, in telophase, while elements of the ER in the poles of the spindle coalesce around the chromosomes to form the new envelope, the advancing edges of those in the middle zone reticulate at the level of the equator to form a close lattice of tubular elements. Within this, which is identified as the phragmoplast, the earliest signs of the cell plate appear in the form of small vesicles. These subsequently grow and fuse to complete the separation of the two protoplasts. Other morphological units apparently participating in mitosis are described. Speculation is provided on the equal division or not of the nuclear envelope and the contribution the envelope fragments make to the ER of the new cell.     

Localization and cation dependence of a Ca2+- or Mg2+-ATPase from electrocytes of Electrophorus electricus, L

Electrocyte membranes of Electrophorus electricus exhibit high ATPase activity, as demonstrated by cytochemical and biochemical techniques. This activity is visualized as electron-dense deposits in electron micrographs, and appears to be localized only at the innervated face of the electrocyte. ATP hydrolysis can be detected cytochemically or biochemically only in the presence of calcium or magnesium. The effects of Ca or Mg on ATPase activity can be described by Michaelis-like functions with similar apparent Km values for Ca and Mg (0.41 mM and 0.23 mM, respectively). Vmax, however, is fivefold higher in the presence of Mg. The effects of the two cations are not additive, and pH dependence of ATP hydrolysis is identical in the presence of Ca or Mg (maximal at pH 8-9). Therefore, it can be concluded that Ca and Mg activate the same enzyme, the differences in Vmax being attributable to influences in kcat.     

Alcohol dehydrogenase (EC 1.1.1.1) isozymes as markers at 2,4-dichlorophenoxyacetic acid × kinetin combinations in callus cultures ofCereus peruvianus (Cactaceae)

Alcohol dehydrogenase (ADH; EC 1.1.1.1) isozymes were investigated in tissue ofCereus peruvianus cultured in different concentrations of 2,4-dichlorophenoxyacetic acid (2,4-D) and kinetin. Five ADH isozymes were detected in starch gel and showed different patterns in seeds, seedlings, calli cultured at 32 and 22°C, and plants regenerated from calli cultured in three 2,4-D and kinetin combinations. Four phenotypes formed by different combinations of ADH-2, ADH-3, ADH-4, and ADH-5 were detected in calli cultured at 32°C and in plants regenerated from calli. ADH-1 isozyme was detected only in calli subcultured for 1 or 2 weeks at 22°C and was indicated as a marker of stress conditions that affect the growth ofC. peruvianus callus tissues in culture. ADH phenotypes with either a higher or a lower number of isozymes were detected in different proportions in the callus tissues cultured in media containing different 2,4-D and kinetin ratios. ADH isozyme patterns were found to be sensitive markers at the highest kinetin concentration or at high kinetin/2,4-D ratios. The results indicate a high correlation between the ADH isozyme patterns and the capacity for regeneration. Thus, ADH isozymes are indicated as good biochemical markers and as a powerful tool for monitoring studies ofC. peruvianus callus cultures.This research was supported by the CNPq.     

Validation of the cumulative or replicate NAA method for the determination of trace elements in biological materials

Biological Trace Element Research - To make the best use of time and facilities, a neutron activation system, fully automatic, including spectrum and data processing, to be used with short-lived...     

A scanning electron microscope study of normal and vitrified leaves from Datura insignis plantlets cultured in vitro

The surface anatomy of normal and vitreous leaves of plantlets obtained from Datura insignis Barb Rodr nodal segment cultures was compared using scanning electron microscopy. Normal and vitrified leaves are similar in several ways. They are both amphistomatic, and have similar distributions of glandular and non-glandular trichomes. Stomata have similar length, diameter and distribution in normal and vitreous plants. Immature stomata, which have closed pores, and plugged stomata, which contain an amorphous material between their guard cells, occur in both normal and vitrified leaves. Normal and vitreous leaves differ in the frequency of normal and abnormal stomata. Normal stomata have kidney-shaped guard cells and resemble closely those found in field-grown plants, whereas abnormal stomata have deformed guard cells. Normal stomata represent approximately 80% of the total number of stomata in normal leaves, but only 7% of the total number of stomata in vitreous leaves. Abnormal stomata represent 90% of the total number in vitreous leaves. The deformation of guard cells could possibly be a mechanical impediment to stomatal function.     

Low Selenium Diet Affects Monoamine Turnover Differentially in Substantia Nigra and Striatum

Abstract: Turnover of dopamine, noradrenaline. serotonin, and their metabolites has been measured in striatum and substantia nigra of adult female rats that were fed control or selenium-deficient diets for 15 days. In addition, the glutathione peroxidase activity has been studied. The most striking result was the increase of dopamine turnover (63%) and 3- methoxytyramine turnover (55%) in substantia nigra between control and experimental animals. On the other hand, no changes were found in the turnover rate of dopamine and its metabolites in the striatum. Likewise, no changes were found in noradrenaline turnover in substantia nigra. In the striatum, there was a significant increase of serotonin turnover versus no change for 5-hydroxy-3-indoleacetic acid. However, in the substantia nigra, serotonin turnover did not show significant changes, whereas 5-hydroxy-3-indoleacetic acid turnover decreased. At the same time, glutathione peroxidase activity significantly decreased in both structures after selenium-deficient diets. These results suggest that a selenium-deficient diet for a short period of time decreases brain protection. principally in the substantia nigra, against oxidative damage.     

Characterization of hemocytes from the marine amphipod Parhyale hawaiensis (Dana 1853): Setting the basis for immunotoxicological studies

Hemocytes are circulating blood cells that play a crucial function in amphipods and other crustacean immune systems. The hemocytes of the marine tropical amphipod Parhyale hawaiensis have been used for the evaluation of DNA damage and micronuclei, but they have not been characterized in the scientific literature. The aim of this study was to describe the hemolymph cells of P. hawaiensis and study their phagocytotic activity. Basic dyes were used to differentiate the cell types and the presence of lipids. The total hemocyte counts (THCs) and the proportion and sizes of the hemocyte types were determined. Hemolymph was exposed to Escherichia coli for verification of the presence of phagocytosis. Three cell types, all containing lipids, were identified in P. hawaiensis: granulocytes (oval shape, 13.4 × 7.6 μm), semi-granulocytes (oval shape, 14.1 × 7.2 μm), and hyalinocytes (round shape, 9.6 × 7.2 μm). Those three cell types were found in different percentages in males (64.8%, 31.1%, and 4.2%) and females (70.1%, 28.2%, and 1.7%). THCs for males were 9007 ± 3800 cells per individual and 4695 ± 1892 cells per individual for females. The cells of E. coli were phagocytized by the hemocytes. Our findings increased the knowledge of hemocytes in P. hawaiensis and is a step forward in using hemocyte-based immune responses as an endpoint in ecotoxicology.