Trace Amounts Of Ca Research Articles

Amylase activity and stability at high and low temperature depending on calcium and other divalent cations.

Since the extracellular amylase from B. caldolyticus had been characterized as a Ca-dependent enzyme, we wanted to determine the function and specificity of this ion, and it's possible significance for the thermophilic properties of the enzyme. The first question concerned the substitution of Ca with regard to the activity at 70 C. Our data show that Sr or other divalent cations can only to a limited extent replace Ca, and that only in presence of Ca full activity can be achieved. When the majority of the binding sites of the subunits are occupied by cations other than Ca, an almost total loss of activity results. The reason for this kind of inactivation was found in the responsibility of Ca for the stability of the enzyme at high temperature. The omission of Ca then leads to an irreversible denaturation of the enzyme, so that after this kind of treatment no activity is detectable at either high or low temperature, which means that the amylase is not a thermostable enzyme in the classical sense. The stabilizing effect of Ca could not be substituted by any other of the cations tested. Experiments concerning the stability of the enzyme at various temperatures in absence of presence of Ca revealed that the enzyme is stable up to 55 C as long as trace amounts of Ca are available. If these are omitted by a chelator, the enzyme becomes unstable between 40 and 45 C. Experiments in which a certain protein concentration range was tested at 40 and 70 C with given concentrations of Ca showed that the stability, and with it the activity, at high temperature is directly related to the amount of Ca available: The more the Ca supply is limited, the less enzyme protein can be kept in the right configuration, and irreversibly denatures as a result. At low temperature, however, the enzyme becomes almost independent of Ca, and the small amounts necessary to obtain full activity can be replaced by other divalent cations. The main conclusions concerning the role of Ca are that at high temperatures it participates in achieving the correct configuration of the thermostable form of the enzyme, and that in this function it is irreplacable. At low temperature it acts as an unspecific cofactor. The other conclusion is that the amylase can exist either as a caldo-active, thermostable, Ca-dependent enzyme, or in a Ca-independent thermostable state with a lower activity.

Zum Calciumbedarf von Oxalatpflanzen

Summary The well-known fact that chemical analysis of plants containing soluble oxalate does not yield any soluble Ca led to the suggestion that such plants avoid Ca by precipitating all of it. Contradictory to these beliefs we have recently found out, that an oxalate-containing cell sap does not exclude that the plants need some dissolved Ca in their plasm. By cultivating Ca-precipitating plants on various solutions we have found that the very presence of oxalate in the plant may cause an especially urgent need of Ca. Tradescantia viridis which contains dissolved oxalate in its immature parts, shows Cadeficiency necroses after an interval of 4–5 weeks, because then the increase of soluble oxalate prevents the Ca-supply to the youngest parts. On the other hand the related Zebrina pendula, which does not produce any remarkable amount of oxalate and normally accumulates a lot of dissolved Ca does not show any Ca-deficiency neeroses when kept on practically Ca-free nutrient solution even after an interval of months. This is because the trace amounts of Ca that are available can be held in their watersoluble state - i. e. physiologically effective. Based on these experiments and on the above mentioned information on Ca-deficiencies of oxalate-containing plants, such as Beta and Lemna, we must no longer accept Iljin's concept of the physiological Calciophobia of the Ca-precipitating plants. His concept lacks the clear differentiation between the ion-contents of cytoplasm and vacuole. (i. e.: between the compartments of metabolism and internal excretion).

The steps between depolarization and the increase in the respiration of frog skeletal muscle.

1. For many years it has been known that when muscles are depolarized by raising [K(+)](out) there is an increase in respiration, even at levels of depolarization below the threshold for a detectable contracture.2. K(+)-stimulated respiration occurs in muscles in which protein synthesis is blocked with puromycin. Stimulation does not depend upon activation of phosphorylase kinase. In muscle poisoned with IIA and kept in N(2), depolarizations below the threshold for contracture cause a fall in creatine phosphate. Apparently an ATPase is activated by depolarization; the resulting ADP is probably the trigger for the increase in oxygen uptake.3. When the T-tubules are destroyed by the glycerol-osmotic shock method depolarization does not produce an increase in respiration.4. Caffeine is known to stimulate respiration at concentrations below the threshold for producing a contracture. Muscles that have been made refractory to stimulation by potassium are still stimulated by caffeine: the action of caffeine is not antagonized by an increase in extracellular Mg(2+). Caffeine must act on a later step in excitation-contraction coupling.5. K(+)-stimulated respiration ultimately depends on the presence of Ca(2+) in the Ringer. However, the Ca(2+) can be replaced by Ni(2+). It is known that Ni(2+) does not activate actomyosin. Ni(2+) is not sequestered by isolated fragments of the sarcoplasmic reticulum. It seems that the Ni(2+) or Ca(2+) in the extracellular solution is required for a superficial step in excitation-contraction coupling.6. Respiration is also often stimulated when muscles are placed in an isotonic sucrose solution, even though the fibres are hyperpolarized. A trace amount of Ca(2+) in the sucrose solution is probably necessary for the response.7. An interaction between Ca(2+) and a superficial membrane receptor appears to be an essential, early step in excitation-contraction coupling.

A Plinthaquult of the Aripo Savannas, North Trinidad II. Mineralogy and Genesis

AbstractThe Aripo Savanna Fine Sand, a Plinthaquult, has developed on water‐transported erosion products derived from the Northern Range in Trinidad. The profile consists of a surface‐bleached layer of 25 cm thickness composed of silt and fine sand, underlain by an intensely red‐ and yellow‐mottled argillic layer. The first 10 cm of this layer has ochreous diffuse mottling and is very rich in Fe. Deeper, the mottles are more distinct and red in color on an almost grey matrix. On exposure, these mottles (plinthite) harden irreversibly to nodules. Chemical and mineralogical properties of nodular material thus formed ranging from 1 to 30 years of age were examined. With time, the nodules become firmer and richer in Fe. The intensity of red coloration within the nodules is directly related to the amount of Fe present. All nodules are very low in Mn; Ti is inversely related to Fe but Ca is evenly distributed throughout all nodular materials regardless of age. No crystalline Fe minerals occur, but lepidocrocite and goethite are present in the ochreous mottles in a thin horizon above the nodule‐producing layer.The soil is derived from micaceous (muscovite) parent materials, but mica content is low; kaolinite derived from mica weathering is the dominant mineral. There are also identifiable amounts of montmorillonite or vermiculite‐type mineral thought to be derived from weathering of mica and representing intermediates in the formation of kaolinite. Cation exchange capacity and surface area values are in accordance with this mineral assemblage. The silt and sand fractions are almost pure quartz. Absence of feldspars in the silt fraction is confirmed by only trace amounts of Ca and Na found by chemical analysis. The data indicate that this soil is perhaps the most weathered of Trinidadian soils.