On the dynamics of exploited populations ofTisbe holothuriae (Copepoda,Harpacticoida)

A total of 30 weekly exploited populations of the harpacticoid copepodTisbe holothuriae Humes were exposed to 148 or 222µg Cd⁺⁺ l^–1, combined with exploitation rates of 10, 30, 50, 70 or 90% under conditions of surplus food supply at 22 °C and 30 S. During the observation period, most populations exhibited distinct U-shaped density trends. Addition of Cd⁺⁺ prolonged and reinforced the downward trends present in the initial periods of the experiments. If population densities, both in control and test populations, fell short of a certain value, the age structures shifted in favour of the nauplii. More pronounced reductions in population densities of the test populations did not result in increased elevations of the nauplius fraction. Within 23 weeks (or 20 generations), the effect of Cd⁺⁺ on population density was counteracted by an acclimation process. No relationship could be established between exploitation rate and observed effects. Erroneous assumptions on the adaptability of parametric methods had led to invalid statements on the dispersion of data published in previous papers of this series. These statements have been revised. Possible limitations of the significance of the results obtained are discussed in some detail.     

On the dynamics of exploited populations ofTisbe holothuriae (Copepoda,Harpacticoidae)

A total of 90, weekly exploited populations of the harpacticoid copepodTisbe holothuriae Humes were exposed to 148, 222, 333, 500, 750 or 1125µg Cd⁺⁺ l^–1, combined with exploitation rates of 10, 30, 50, 70 or 90% under conditions of surplus food supply at 22° C and 30 S. All populations exposed to concentrations down to 500µg Cd⁺⁺ l^–1 and 3 populations (out of 15) exposed to 333µg l^–1 became extinct within the experimental period of 30 weeks. Survival time significantly depended on concentration. A recovery phase from an initially high mortality preceded eventual population extinction after adding 500µg Cd⁺⁺ l^–1. In the initial phase, higher nauplii mortality prevailed. During these experiments on acute intoxication, no relationship could be established between survival and exploitation rate. However, experiments on the effects of stepwise increases in Cd concentration (results not yet published) produced evidence of such a relationship. In spite of increased mortality, no significant numbers of dead copepods were detected in weekly samples because of their rapid decomposition and cannibalism, which depends on the amount of food available. Sampling regimes of 5 times per week yielded significant numbers of dead individuals.     

Zur Dynamik exploitierter Populationen vonTisbe holothuriae (Copepoda,Harpacticoida)

In weekly exploited populations of the harpacticoid copepodTisbe holothuriae Humes, effects of exploitation rate on population density, age distribution, growth, as well as numerical and biomass yields were studied under conditions of surplus food supply at 22° C and 30 ‰ S. Increase of exploitation rate lowered the adult plus copepodid density and raised the density of nauplii, thus shifting the age distribution in favour of the nauplii. Total population density was almost equal at exploitation rates of 0.10, 0.50 and 0.70, but lower at rates of 0.30 and 0.90. Experiments, which have not yet been completed, have shown a higher resistance against the toxic effect of cadmium in populations exploited at rates of 0.30 or 0.90; populations exploited at the lower rate displayed a lesser degree of resistance than populations exploited at the rate of 0.90. Variability of densities was least at intermediate exploitation rates, whereas the variability of the age structure and the intrinsic rate of natural increase was less at higher rates, indicating smaller fluctuations in the ratio of the regulating variables mortality and fecundity with increasing exploitation. The assumption is made that an appropriate exploitation rate contributes to the achievement of favourable culture conditions for copepods, which are subjected to intense predation in natural populations. Within the range of the exploitation rates selected, biomass yields of nauplii and adults plus copepodids were approximately proportional to exploitation rate; therefore, the maximum rate sustainable by aTisbe holothuriae population cannot be established. From data on adult numerical yield, however, it may be concluded that exploitation rates exceeding 0.90 will not result in increased productivity.     

Zur Dynamik exploitierter Populationen vonTisbe holothuriae (Copepoda,Harpacticoida)

In weekly exploited populations of the harpacticoid copepodTisbe holothuriae Humes, the dynamics of population development and the effect of the rate of water renewal were studied under conditions of surplus food supply, constant temperature (22° C) and salinity (30 ‰). At exploitation rates of 10, 30, 50, 70 or 90% per week, the populations maintained stable mean populations sizes. None of the populations established stationary equilibria. Reduced rates of water renewal resulted in a reduction of mean population density, in the course of which the density of adults plus copepodids was diminished to a lesser degree when low, as opposed to high, percentages of specimens were removed. The density of nauplii was distinctly reduced at all exploitation levels. The age structure shifted in favour of the adults and copepodids and was subject to higher variability at moderate exploitation rates and lowered rate of water renewal. To avoid and to remove difficulties inherent to current concepts of population dynamics, the populations were regarded as a component of a feedback control system, and an attempt has been made to describe the observed processes by analogy to technical control systems. According to not yet completed series of experiments, populations undergoing higher exploitation rates seem to compensate more succesfully for perturbations of their environment, than populations exploited at lower rates.     

Enhanced cadmium cytotoxicity in A549 cells with reduced glutathione levels is due to neither enhanced cadmium accumulation nor reduced metallothionein synthesis

Glutathione (GSH) depletion sensitizes human lung carcinoma (A549-727) cells to the cytotoxic effects of Cd⁺⁺. The effects of GSH depletion on Cd⁺⁺ accumulation and Cd⁺-induced metallothionein (MT) content were investigated to determine the possible role of these Cd⁺⁺ responses in the sensitization process. Cellular GSH was depleted to 20% to 25% of control levels with buthionine sulfoximine (BSO), or diethyl maleate (DEM), respectively. Neither treatment significantly affected Cd⁺⁺-induced accumulation of exogenous³⁵s-cysteine into intracellular MT in a dose-dependent fashion. The results indicate that neither enhanced Cd⁺⁺ accumulation nor reduced MT synthesis plays a primary role in affecting enhanced Cd⁺⁺ cytotoxicity in A549 cells with reduced GSH levels. Although BSO inhibition of GSH synthesis enhanced MT synthesis, it sensitized the cells to Cd⁺⁺, which suggests an additive effect of GSH and MT in cadmium cytoprotection. This observation also raises the possibility that intracellular cysteine levels limit Cd⁺⁺-induced MT accumulation rates.Abbreviations GSH glutathione - MT metallothionein - BSO DL-buthionine-[S,R]-sulfoximine - DMSO dimethyl sulfoximine - DEM diethyl maleate - NP-40 nonidet-P40 - PBS phosphate buffered saline - HBSS Hank's balanced salt solution - DTT dithiothreitol 3. This work was presented in part at the 72nd Annual Meeting of the Federation of American Societies for Experimental Biology, Las Vegas, Nevada, May 1–5, 1988.     

Effect of cellular glutathione depletion on cadmium-induced cytotoxicity in human lung carcinoma cells

The effect of glutathione depletion on cellular toxicity of cadmium was investigated in a subpopulation (T27) of human lung carcinoma A549 cells with coordinately high glutathione levels and Cd⁺⁺-resistance. Cellular glutathione levels were depleted by exposing the cells to diethyl maleate or buthionine sulfoximine. Depletion was dose-dependent. Exposure of the cells to 0.5 mM diethyl maleate for 4 hours or to 10 mM buthionine sulfoximine for 8 hours eliminated the threshold for Cd⁺⁺ cytotoxic effect and deccreased the LD_50S. Cells that were pretreated with 0.5 mM diethyl maleate or 10 mM buthionine sulfoximine and then exposed to these same concentrations of diethyl maleate or buthionine sulfoximine during the subsequent assay for colony forming efficiency produced no colonies, reflecting an enhanced sensitivity to these agents at low cell density. Diethyl maleate was found to be more cytotoxic than buthionine sulfoximine. Synergistic cytotoxic effects were observed in the response of diethyl maleate pretreated cells exposed to Cd⁺⁺. Thus the results demostrated that depletion of most cellular glutathione in A549-T27 cells prior to Cd⁺⁺ exposure sensitizes them to the agent's cytotoxic effects. Glutathione thus may be involved in modulating the early cellular Cd⁺⁺ cytotoxic response. Comparison of reduced glutathione levels and of Cd⁺⁺ cytotoxic responses in buthionine sulfoximine-treated A549-T27 cells with those levels in other, untreated normal and tumor-derived cells suggests that the higher level of glutathione in A549-T27 is not the sole determinant of its higher level of Cd⁺⁺ resistance.Abbreviations BSO DL-buthionine-(R,S)-sulfoximine - DEM diethyl maleate - DMSO dimethyl sulfoxide - GSH reduced glutathione - MT metallothionein     

Selection and characterization of cadmium-resistant suspension cultures of the wild tomato Lycopersicon peruvianum

Suspension cultures of Lycopersicon peruvianum were selected for resistance to cadmium by stepwise exposure to increasing concentrations of cadmium sulfate. Resistant cells grow in 1500 micromolar Cd⁺⁺. This resistance was retained for thirty generations without selection. Both resistant and parental sensitive cultures take up Cd⁺⁺ at similar rates and to the same final levels. Exposure of sensitive or resistant cultures to Cd⁺⁺, Cu⁺⁺, or Zn⁺⁺ leads to the intracellular accumulation of a low molecular weight, cysteine-rich, cadmium-binding protein. This metallothionein is induced over fifteen fold by 100 M cadmium and builds up to about five fold higher levels in the resistant cultures.Abbreviations Cd⁺⁺ divalent cadmium ion - Cu⁺⁺ divalent copper ion - Zn⁺⁺ divalent zinc ion - BA benzyl adenine - 2,4-D 2,4-dichlorophenoxyacetic acid - IAA indole-acetic acid     

Effects of Cd++ on short-circuit current across epithelial membranes

Summary Cadmium ion (Cd⁺⁺) was found not to inhibit active sodium transport across the isolated frog skin when added in 10^–3 m concentration to the basal-lateral surface. The same Cd⁺⁺ concentration similarly had no effect on Na⁺ transport across the isolated epithelial cell layer from the frog skin, although this dose of Cd⁺⁺ did inhibit Na⁺ transport across the frog urinary bladder and large intestine. When 10^–3 m Cd⁺⁺ was added to the apical surface of the isolated frog skin or to the isolated epithelial cells from the frog skin, sodium transport was reversibly stimulated, in contrast to the irreversible inhibition noted above. If equimolar cysteine was added with Cd⁺⁺ to the apical surface of the skin, however, active Na⁺ transport was irreversibly inhibited. In conjunction with the inhibition produced by equimolar Cd⁺⁺ and cysteine, isotopic Cd⁺⁺ permeation into the tissue was three times higher when added with cysteine than in the absence of cysteine. Thus, the effects of Cd⁺⁺ on epithelial Na⁺ transport is variable according to the epithelium studied and the presence of potential carrier molecules.     

Cd++ inhibits EGF-induced DNA synthesis but not EGF induced myc mRNA accumulation in serum starved NRK-49F cells

Cd⁺⁺ inhibits EGF-induced ³H-thymidine incorporation in serum deprived NRK-49F cells in a dose dependent pattern. The underlying mechanisms for this inhibition are largely unknown. EGF-induced myc mRNA accumulation in NRK-49F cells and the effects of Cd⁺⁺ on this response were examined under conditions that result in partial or complete inhibition of EGF-induced DNA synthesis. It was found that doses of Cd⁺⁺ that inhibit EGF-induced DNA synthesis do not inhibit EGF-induced protein synthesis and myc mRNA accumulation. Cd⁺⁺ doses of 0.5 µM and 1 µM were found actually to increase EGF-induced myc mRNA accumulation and amino acid incorporation. These results show that the effect of Cd⁺⁺ on EGF-induced DNA synthesis is not due to inhibition of entrance into G₁, but rather that Cd⁺⁺ acts on events subsequent to myc accumulation; that is, events associated with either G₁ progression, entry into S or DNA synthesis.Abbreviations EGF Epidermal Growth Factor - ³HTdr Tritium thymidine - MeAIB Methylaminoisobutyrate     

Cadmium produces a delayed mitogenic response and modulates the EGF response in quiescent NRK cells

Recent studies have shown that cadmium, at subtoxic levels, may induce a response characteristic of that elicited by a type of growth factor that supports the anchorage independent growth of cells that are not fully transformed. That is, Cd⁺⁺ was found to replace transforming growth factor beta in supporting soft agar growth of NRK-49F cells. To tes the extent to which Cd⁺⁺ further mimics transforming growth factor beta in its effects and to establish response patterns that suggest possible molecular mechnisms of action, we have determined the effects of Cd⁺⁺ and/or epidermal growth factor (EGF) on DNA synthesis in quiescent NRK-49F cells. We found that subtoxic doses of Cd⁺⁺ modulate EGF-induced DNA synthesis in a dose-dependent fashion. Although Cd⁺⁺ effects on early (16–24 hr) EGF-induced DNA synthesis are primarily inhibitory, later effects involve stimulation as well. Subtoxic doses of Cd⁺⁺ did not stimulate DNA synthesis in quiescent cells within 24 hr of addition. At later times (40 or 64 hr), however, an increase in DNA synthesis of up to threefold was induced by 0.25 M Cd⁺⁺. This pattern of mitogenic response, involving inhibition of early growth-factor induced DNA synthesis and stimulation of late DNA synthesis, is consistent with that reported to be effected in some instances by transforming growth factor beta. Because a defined pattern of gene expression also is associated with the mitogenic responses to transforming growth factor beta, future studies at the molecular level can definitively test the degree to which Cd⁺⁺ and transforming growth factor beta effects are common.Abbreviations CFE colony forming efficiency - EGF epidermal growth factor - MT metallothionein - PGDF paltelet derived growth factor - TGF transforming growth factor     

Effects of Cd++ on short-circuit current across epithelial membranes

Summary Cadmium ion (Cd⁺⁺) significantly increased potential difference (PD) and short-circuit current (SCC) across isolated frog skin when added to the outside Ringer's solution at 10^–4, 10^–3 and 5×10^–3 m concentration. Resistance was reduced by 10^–4 m Cd⁺⁺ but not significantly changed by the higher concentrations. When SCC was first stimulated by vasopressin, 10^–4 and 10^–3 m Cd⁺⁺ produced additive stimulation which was reversible by washing with Cd⁺⁺-free Ringer's. If SCC was first stimulated by Cd⁺⁺, further stimulation by vasopressin was additive with 10^–4 m Cd⁺⁺ but completely inhibited by 10^–3 m Cd⁺⁺. Elevating the calcium ion (Ca⁺⁺) concentration of the outer Ringer's from 10^–3 m to 5×10^–3 m or 10^–2 m prior to Cd⁺⁺ treatment did not reduce the magnitude of SCC stimulation by Cd⁺⁺. Removal of Ca⁺⁺ from the outside Ringer's with 2×10^–3 m EDTA increased SCC as predicted. Subsequent addition of 5×10^–3 m Cd⁺⁺ drastically reduced SCC below control levels while equimolar concentrations of Cd⁺⁺ and EDTA reduced SCC only to control levels. These results suggest that Cd⁺⁺ interacts with the components of the apical plasma membranes of epithelial cells which are associated with the stimulation of SCC by vasopressin and Ca⁺⁺ removal and may be a useful probe for elucidating these components.     

Levels of ornithine decarboxylase activation used as a simple marker of metal induced growth arrest in tissue culture.

Exposure of proliferating cells to specific water solube metal compounds at 0.1 or 1.0 mM concentrations inhibited cell growth and also depressed the induction of ornithine decarboxylase, an enzyme which is tightly coupled to the initiation of cell growth. Salts of Co⁺⁺, Ni⁺⁺, Cu⁺⁺, Cr⁺⁶ and Cd⁺⁺ significantly reduced incorporation of radiolabeled leucine, thymidine or uridine into trichloroacetic acid insoluble material, inhibited the doubling of Chinese hamster ovary cells, and blocked the the induction of ornithine decarboxylase. The addition of similar concentrations of other metals such as Fe⁺⁺, K⁺, Mg⁺⁺, Pb⁺⁺, Ca⁺⁺ or Sn⁺⁺ had no effect on ODC induction and also did not inhibit the other parameters associated with cell proliferation which were measured. These results suggest that ornithine decarboxylase induction can be used as a marker of metal induced growth arrest.     

The role of calcium in excitation-contraction coupling of lobster muscle

Potassium contractures were induced in lobster muscle bundles under conditions which produced varying KCl fluxes into the fibers. The presence or absence of chloride fluxes during depolarization by high concentrations of potassium, had no effect on the tensions developed. The curve relating tension to the membrane potential had a typical sigmoid shape with an apparent "threshold" for tension at -60 mv. Soaking the muscles in low (0.1 mM) calcium salines for 30 min completely eliminated the potassium contractures but the caffeine contractures were only slightly reduced under these conditions. The potassium contracture could be completely restored in less than 2 min by return of the calcium ions to the saline. Evidence is presented for independent, superficial, and deep calcium sites; the superficial sites appear to be involved in the coupling mechanisms associated with potassium contractures. These sites are highly selective for Ca⁺⁺, and attempts to substitute either Cd⁺⁺, Co⁺⁺, Mg⁺⁺, Ba⁺⁺, or Sr⁺⁺ for Ca⁺⁺ were unsuccessful. However, K⁺ appeared to compete with Ca⁺⁺ for these sites, and the evoked tension could be reduced by prestimulation of the muscle fibers with high K⁺ salines. The results of studies on the influx of ⁴⁵Ca during potassium contractures were compatible with the view of muscle activation by the entry of extracellular calcium.     

The SbMT-2 Gene from a Halophyte Confers Abiotic Stress Tolerance and Modulates ROS Scavenging in Transgenic Tobacco

Heavy metals are common pollutants of the coastal saline area and Salicornia brachiata an extreme halophyte is frequently exposed to various abiotic stresses including heavy metals. The SbMT-2 gene was cloned and transformed to tobacco for the functional validation. Transgenic tobacco lines (L2, L4, L6 and L13) showed significantly enhanced salt (NaCl), osmotic (PEG) and metals (Zn⁺⁺, Cu⁺⁺ and Cd⁺⁺) tolerance compared to WT plants. Transgenic lines did not show any morphological variation and had enhanced growth parameters viz. shoot length, root length, fresh weight and dry weight. High seed germination percentage, chlorophyll content, relative water content, electrolytic leakage and membrane stability index confirmed that transgenic lines performed better under salt (NaCl), osmotic (PEG) and metals (Zn⁺⁺, Cu⁺⁺ and Cd⁺⁺) stress conditions compared to WT plants. Proline, H₂O₂ and lipid peroxidation (MDA) analyses suggested the role of SbMT-2 in cellular homeostasis and H₂O₂ detoxification. Furthermore in vivo localization of H₂O₂ and O₂ ⁻; and elevated expression of key antioxidant enzyme encoding genes, SOD, POD and APX evident the possible role of SbMT-2 in ROS scavenging/detoxification mechanism. Transgenic lines showed accumulation of Cu⁺⁺ and Cd⁺⁺ in root while Zn⁺⁺ in stem under stress condition. Under control (unstressed) condition, Zn⁺⁺ was accumulated more in root but accumulation of Zn⁺⁺ in stem under stress condition suggested that SbMT-2 may involve in the selective translocation of Zn⁺⁺ from root to stem. This observation was further supported by the up-regulation of zinc transporter encoding genes NtZIP1 and NtHMA-A under metal ion stress condition. The study suggested that SbMT-2 modulates ROS scavenging and is a potential candidate to be used for phytoremediation and imparting stress tolerance.     

Effects of soil-added Cl on growth ofAndropogon scoparius and possible implications for heavy metal research

Soil additions of Cl^–, as NaCl, over the 0 to 400 ppm Cl^– range did not affect germination forAndropogon scoparius. Height and top dry weight were significantly reduced by 300 ppm soil added Cl^–. Although not conclusive, these results did indicate that growth and germination effects reported for Cd⁺⁺, added as CdCl₂, are probably due to Cd⁺⁺ rather than to a Cl^– or salt effect. Reported Pb⁺⁺ effects, where Pb⁺⁺ is added as PbCl₂, however may be at least partially due to a Cl^– or salt effect.Contribution from Purdue University Agricultural Experiment Station, West Lafayette, Indiana 47907. AES Journal No. 6934. This work was supported by federal funds from the National Science Foundation—RANN Program.     

Cation activation of desoxyribonuclease

The activation of desoxyribonuclease on desoxyribonucleate, known to occur with Mg⁺⁺ and Mn⁺⁺, has been shown to occur equally well with Co⁺⁺, to nearly the same extent with Fe⁺⁺, and to a lesser extent with Ca⁺⁺, Ba⁺⁺, Sr⁺⁺, Ni⁺⁺, Cd⁺⁺, and Zn⁺⁺. The conditions under which the optimal activation is revealed vary among these ions. Thus, Mg⁺⁺, Mn⁺⁺, and Co⁺⁺ may show marked activation under conditions in which Fe⁺⁺ is nearly ineffective. Since too high a concentration of an ion may be as ineffective as too little, concentration-activation curves were determined for each ion. Per micromole of nucleic acid phosphorus, the optimal effective amount of each ion in micromoles is as follows: Mg⁺⁺ 3, Mn⁺⁺ 3, Co⁺⁺ 3, Fe⁺⁺ 0.3, Ni⁺⁺ 0.3, Ba⁺⁺ 1.7, Ca⁺⁺ 3, Sr⁺⁺ 3, Zn⁺⁺ 0.3, and Cd⁺⁺ 0.3.The optimum pH for the activation with Mg⁺⁺, Co⁺⁺, and Ca⁺⁺ is about 6.5, that with Fe⁺⁺ is at 5.7, while Mn⁺⁺ shows two optima at pH 6.8 and 8.0.Experiments conducted in Pyrex and in quartz vessels showed the same results, and indicated that there was no activation of desoxy-ribonuclease in the absence of added salts.     

Mechanisms for Intracellular Calcium Regulation in Heart : I. Stopped-Flow Measurements of Ca++ Uptake by Cardiac Mitochondria

Initial velocities of energy-dependent Ca⁺⁺ uptake were measured by stopped-flow and dual-wavelength techniques in mitochondria isolated from hearts of rats, guinea pigs, squirrels, pigeons, and frogs. The rate of Ca⁺⁺ uptake by rat heart mitochondria was 0.05 nmol/mg/s at 5 µM Ca⁺⁺ and increased sigmoidally to 8 nmol/mg/s at 200 µM Ca⁺⁺. A Hill plot of the data yields a straight line with slope n of 2, indicating a cooperativity for Ca⁺⁺ transport in cardiac mitochondria. Comparable rates of Ca⁺⁺ uptake and sigmoidal plots were obtained with mitochondria from other mammalian hearts. On the other hand, the rates of Ca⁺⁺ uptake by frog heart mitochondria were higher at any Ca⁺⁺ concentrations. The half-maximal rate of Ca⁺⁺ transport was observed at 30, 60, 72, 87, 92 µM Ca⁺⁺ for cardiac mitochondria from frog, squirrel, pigeon, guinea pig, and rat, respectively. The sigmoidicity and the high apparent K_m render mitochondrial Ca⁺⁺ uptake slow below 10 µM. At these concentrations the rate of Ca⁺⁺ uptake by cardiac mitochondria in vitro and the amount of mitochondria present in the heart are not consistent with the amount of Ca⁺⁺ to be sequestered in vivo during heart relaxation. Therefore, it appears that, at least in mammalian hearts, the energy-linked transport of Ca⁺⁺ by mitochondria is inadequate for regulating the beat-to-beat Ca⁺⁺ cycle. The results obtained and the proposed cooperativity for mitochondrial Ca⁺⁺ uptake are discussed in terms of physiological regulation of intracellular Ca⁺⁺ homeostasis in cardiac cells.     

Effects of calcium and potassium channel blockers on changes in transepithelial potential and spike responses in Lorenzi ampullary electroreceptors in Raja clavata

The effects of TEA, 4-AP, Co⁺⁺, Cd⁺⁺, Cs⁺, EDTA, and verapamil on the sensory epithelium of ampullae of Lorenzini were studied inRaja clavata (Black Sea skate). During voltage clamping, transepithelial application of TEA to the basal surface caused oscillations in transepithelial potentials in response to presentation of an excitatory stimulus, which had been suppressed by Co⁺⁺, Cd⁺⁺, and EDTA. Application of Cs⁺ was followed by complete or partial suppression of spike response adaptation. When applied to the apical epithelial surface, TEA produced an increase in spike response to stimulation and highly accelerated adaption. No substantial changes took place after apical application of Co⁺⁺, Cd⁺⁺, and verapamil. The mechanisms of these phenomena are discussed.Deceased.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 17, No. 5, pp. 652–659, September–October, 1985.     

Studies on the Pentose Isomerases of Lactic Acid Bacteria

d-Xylose isomerase requires manganese ions for its action, but l-arabinose isomerase has a less specific on metal requirement. l-Arabinose isomerase is activated by addition of Mn⁺⁺ or Co⁺⁺, less effectively by addition of Zn⁺⁺, Ca⁺⁺, Mg⁺⁺, Sr⁺⁺ or Cd⁺⁺. Moreover, manganese and potassium ions for d-xylose isomerase, and manganese and cobaltous ions for l-arabinose isomerase were also shown to have protective effect on respective enzymes against thermal inactivation.