Exchange Velocity Research Articles

A method for defining steady-state unidirectional fluxes through branched chemical, osmotic and chemiosmotic reactions

A general mathematical technique is described for deriving analytical expressions and obtaining numerical solutions for the steady-state unidirectional fluxes between two chemical states via any set of intermediate states present within any hypothetical system of unbranched or branched and overlapping elementary processes. The technique is a restricted application of the theory of Markov processes with conditional probabilities being assigned to the chemical state transitions constituting the system of reactions. While, in principle, the technique requires the summation of an infinite power series of a matrix defining the conditional probabilities of single state transitions, the power series is evaluated by means of the Taylor series expansion for matrices. As this technique allows isotopic exchange velocity equations to be derived from systems of reactions in which no distinction between the labelled and unlabelled species is required it provides a distinct and independent alternative to previously proposed methods. The technique is illustrated by application to a mechanism for second-order carrier-mediated transport.

Isotopic versus micrometeorologic ocean CO2 fluxes: A serious conflict

Eddy correlation measurements over the ocean give CO2 fluxes an order of magnitude or more larger than expected from mass balance measurements using radiocarbon and radon 222. In particular, Smith and Jones (1985) reported large upward and downward fluxes in a surf zone at supersaturations of 15% and attributed them to the equilibration of bubbles at elevated pressures. They argue that even on the open ocean such bubble injection may create steady state CO2 supersaturations and that inferences of fluxes based on air‐sea pCO2 differences and radon exchange velocities must be made with caution. We defend the global average CO2 exchange rate determined by three independent radioisotopic means: prebomb radiocarbon inventories; global surveys of mixed layer radon deficits; and oceanic uptake of bomb‐produced radiocarbon. We argue that laboratory and lake data do not lead one to expect fluxes as large as reported from the eddy correlation technique; that the radon method of determining exchange velocities is indeed useful for estimating CO2 fluxes; that supersaturations of CO2 due to bubble injection on the open ocean are negligible; that the hypothesis that Smith and Jones advance cannot account for the fluxes that they report; and that the pCO2 values reported by Smith and Jones are likely to be systematically much too high. The CO2 fluxes for the ocean measured to date by the micrometeorological method can be reconciled with neither the observed concentrations of radioisotopes of radon and carbon in the oceans nor the tracer experiments carried out in lakes and in wind/wave tunnels.

A 1H-NMR study of the activity expressed by lactate dehydrogenase in the human erythrocyte.

The activity expressed by lactate dehydrogenase in the human erythrocyte has been compared with the activity displayed by the isolated enzyme in vitro. Enzyme activity was measured by using 1H spin-echo NMR to measure non-invasively the velocity of hydrogen label exchange between the C-2 positions of two methyl-labelled lactate species. This method has significant advantages over a method which has been described previously. The exchange velocity observed in the cell was much lower than that expected based on a comparison with measurements of the exchange velocity in vitro under conditions thought to simulate the intracellular environment. Measurements of enzyme inhibition in cell extracts suggest that the low intracellular activity is due to inhibition of the enzyme by low-molecular-mass compounds present in the cell.

Modulation of ATP-dependent calcium extrusion and Na +/Ca 2+ exchange across rat cardiac sarcolemma by calcium antagonists

The calcium antagonists verapamil, bepridil, nifedipine and nimodipine inhibited ATP-dependent 45Ca 2+ uptake in purified rat ventricular sarcolemma vesicles dose dependently. This inhibition was preceded by a slight stimulation in the case of the two dihydropyridines, but not with bepridil and verapamil. In contrast, Na +/Ca 2+ exchange was only inhibited by verapamil and bepridil and not affected by the dihydropyridines. The steepness of the inhibition curves was significantly different for the two processes. No stereoselectivity was found with either process for inhibition by the verapamil enantiomers. Inhibition of the exchange was not due to a decrease of the exchange velocity but to a decrease in exchange capacity. Variation of the antagonist preincubation time did not modify the inhibition of the uptake. The results indicate that two different sites, located at the inner surface of the sarcolemma are involved in the modulation of the ATP-dependent uptake and the Na +/Ca 2+ exchange. However, the possibility cannot be ruled out that inhibition of the exchange process is also mediated by an extracellularly located site.

The Rockall slope current and shelf-edge processes

SynopsisRecent knowledge of physical-oceanographic processes is reviewed for the eastern shelf-edge boundary of the Rockall Channel.A year-round northward current flows along the steep continental slope. Mean currents vary from 3 to 30cm/s, generally increasing northwards, but estimates of transport inshore of the 2000 m depth contour are much more consistent, averaging about 1·5 × 106m3/s. The current is thought to be forced largely by a long-shelf pressure gradient, associated with large-scale N-S density variations in the upper ocean.Although cross-slope changes of temperature and salinity are much less than occur, for example, east of the U.S.A., cross-slope exchange velocities appear to be only around 2cm/s (1/5 of long-slope fluctuations). There is a sharp change between winter-cooled water on the shelf and adjacent slope water. Upwelling against the upper continental slope may occur following northerly long-slope winds. Tidal currents and surges depend strongly on continental shelf wave properties. At near-diurnal frequencies, and in response to winds of short scale (< 100 km), clockwise-rotating currents near the shelf break are expected, especially where the shelf is broadest. Tidal currents show this character.Internal tides are significant; any non-linearity is most likely when stratification is present but weak. Bottom stirring has been observed, and may be important at some depth (where the bottom slope becomes as steep as the semi-diurnal internal characteristics) almost everywhere around the Rockall Channel. The energetic internal waves should contribute significant internal mixing as they approach the shelf break, intensify and dissipate.

Isotope-exchange enhancement studies of Escherichia coli glutamine synthetase.

Isotope-exchange enhancement studies, a variation on positional isotope-exchange enhancement as described by Raushel and Garrard [Raushel, F. M., & Garrard, L. J. (1984) Biochemistry 23, 1791-1795], are used to establish the point in the biosynthetic reaction of Escherichia coli glutamine synthetase at which gamma-glutamyl phosphate is formed. In these experiments, the behavior of the reverse biosynthetic reaction, i.e., the reaction of ADP, L-glutamine, and phosphate to form NH4+, L-glutamate, and ATP, is examined as a function of the concentration of ammonium ion. By varying the concentration of NH4+, the ratio of the velocity of isotope exchange to the velocity of net reaction, as measured by the rate of 18O depletion from labeled phosphate and the rate of production of L-glutamate, respectively, can be modulated in a mechanism-dependent manner. Evidence is presented demonstrating the presence of a branch point in the mechanism. The enzyme-ATP-glutamate complex may partition in two ways, one involving binding of ammonium ion and the other involving the chemical transformation to form the enzyme-ADP-gamma-glutamyl phosphate complex. The alternate pathways then rejoin upon formation of the enzyme-ADP-NH4+-gamma-glutamyl phosphate complex. Because of the branch point, there is no absolute requirement that ammonium ion be absent or present in order for the formation of gamma-glutamyl phosphate to occur. At high concentrations of ammonia, one pathway through the branch can be eliminated, effectively making that portion of the pathway ordered, with ATP, L-glutamate, and NH4+ binding consistent with our previously reported steady-state kinetic mechanism [Meek, T. D., & Villafranca, J. J. (1980) Biochemistry 19, 5513-5519].

Kinetics of nucleoside transport in human erythrocytes. Alterations during blood preservation

The transmembrane equilibration of radiolabeled uridine was measured by rapid kinetic techniques in human erythrocytes from freshly drawn blood and in the same cells during conventional storage of the blood as well as in cells from outdated blood. Our results confirm earlier reports that the maximum velocity of uridine equilibrium exchange ( V ee) at 25°C is about 30% lower in outdated than fresh red cells, whereas the opposite is the case for the Michaelis-Menten constant for equilibrium exchange ( K ee), and that maximum zero- trans efflux ( V 21 zt) is about 4-times greater than maximum zero- trans influx ( V 12 zt) in outdated cells (directional asymmetry), whereas they are about the same in fresh red cells. At 25°C, the nucleoside-loaded carrier of fresh cells moves on the average 6-times more rapidly than the empty carrier, whereas the differential mobility of loaded and empty carrier from outdated cells is about 15-fold. Our results also show that greater efflux than influx in outdated cells is not due to a general leakiness of outdated cells, that the differences in kinetic properties of the transporter developed during the first two weeks of blood storage and that the differences are greatly amplified when transport is measured at 5°C rather than 25°C. At 5°C, the loaded carrier from outdated red cells moves about 325-times more rapidly than the empty carrier and maximum zero- trans efflux exceeds maximum zero- trans influx about 14-times, whereas the transport of fresh cells exhibits directional symmetry just as at 25°C. The changes in kinetic properties of transport induced by temperature and storage are probably related to structural alterations in the plasma membrane and suggest that the operation of carrier is subject to modification by the membrane environment. Other results show that the kinetics of the sugar transport of human red cells is not affected in the same manner by blood storage as those of the nucleoside transporter.

Effect of temperature on kinetics and differential mobility of empty and loaded nucleoside transporter of human erythrocytes.

The transmembrane equilibration of [3H]uridine was measured in human erythrocytes as a function of temperature using rapid kinetic techniques. Arrhenius plots of the maximum velocity of equilibrium exchange were continuous between 5 and 30 degrees C (Ea = 17-20 kcal/mol), but the increase in velocity with increase in temperature leveled off above 30 degrees C. This leveling off did not reflect heat inactivation of the carrier since transport activity was stable for 3 h at 37 degrees C. Transmembrane equilibration of uridine in equilibrium exchange and zero-trans modes at 5, 15, 25, and 35 degrees C conformed to appropriate integrated rate equations derived for the simple transporter. The nucleoside transporter exhibited directional symmetry, but the loaded carrier moved on the average 5 times more rapidly than the empty carrier at 15, 25, and 35 degrees C, but 25-40 times faster at 5 degrees C. This marked shift in differential mobility of loaded and empty carrier between 15 and 5 degrees C was entirely attributable to an impairment of mobility of empty carrier. The Michaelis-Menten constant for equilibrium exchange increased about 3-fold with increase in temperature between 5 and 35 degrees C. The van't Hoff plot of the values was approximately linear and yielded an estimate of the enthalpy of carrier:substrate dissociation of 7.8 kcal/mol.

Proton NMR measurements of hydrogen exchange at the C-3 position of 3-hydroxybutyrate in suspensions of rat liver mitochondria

Rat liver mitochondria suspended in buffer made with 2H 2O catalyse exchange of the C-3 proton of added D-3-hydroxybutyrate with solvent deuterons. The kinetics of this process can be followed using spin-echo proton NMR. The observed isotope exchange velocity is sensitive to the activity of D-3-hydroxybutyrate dehydrogenase, which is an integral protein of the inner mitochondrial membrane. A method is described which can be used to obtain the specific isotope exchange velocity of the enzyme in the intact mitochondrion.

Sodium-calcium exchange in dog heart mitochondria: effects of ischemia and verapamil.

Na+ - Ca2+ exchange was studied in two preparations of dog heart mitochondria isolated from normal and ischemic muscle following occlusion of the circumflex (CFX) coronary artery with or without prior verapamil infusion. Na+ - Ca2+ exchange in mitochondria isolated using polytron homogenization showed sigmoidal kinetics with phosphate, whereas mitochondria isolated using gentle nagarse treatment showed hyperbolic kinetics and a Vmax 60% greater than the polytron preparation. Nagarse did not alter the sigmoidal kinetics or exchange velocities of the polytron mitochondria observed with phosphate. With acetate, both preparations exhibited hyperbolic kinetics, and the sodium required for half-maximum activity was increased. Verapamil inhibited Na+ - Ca2+ exchange in both preparations with phosphate, but not with acetate. Thirty or sixty minutes of acute ischemia following CFX occlusion produced significant epicardial surface S-T elevation in the ischemic area and a decrease in myocardial segment shortening. Na+ - Ca2+ exchange of both ischemic preparations was depressed, and the kinetics of the polytron preparation changed to hyperbolic. Pretreatment of the experimental animals with verapamil (0.3 mg/kg) before 60 min of ischemia protected the exchange rates in both preparations, and the sigmoidicity of the polytron mitochondria was retained.

Nucleoside transport in human erythrocytes. A simple carrier with directional symmetry and differential mobility of loaded and empty carrier.

Rapid kinetic techniques were employed to measure the transport of uridine and thymidine in human erythrocytes in zero-trans entry and exist and equilibrium exchange procedures. The kinetic parameters of transport were computed by fitting appropriate integrated rate equations to time courses of transmembrane equilibration of radiolabeled substrate. Transport of uridine and thymidine conformed to the simple carrier model with directional symmetry, but differential mobility of loaded and empty carrier. As was apparent from comparison of zero-trans influx and equilibrium exchange flux, the loaded carrier moved 3 to 18 times faster than the empty carrier in batches of erythrocytes obtained from different individuals. The maximum equilibrium exchange velocities also differed for different batches of erythrocytes. Storage of the cells at 4 degrees C for 4 days or treatment of cells with oxidizing or reducing agents or suspension in hypotonic solutions had no effect on the kinetic properties of the nucleoside transporter. All natural ribo- and deoxyribonucleosides tested when present on the trans side at concentrations well above the Michaelis-Menten constant for transport accelerated the influx and efflux of uridine and inhibited uridine influx when present at these concentrations on the cis side, but nucleobases had no significant effect.

Combined effects of ATP and phosphate on rubidium exchange mediated by Na-K-ATPase reconstituted into phospholipid vesicles.

1. Phospholipid vesicles reconstituted with Na-K-ATPase show an (ATP+phosphate)-stimulated Rb-Rb exchange, with properties similar to the K-K exchange of human red cells. This includes a rate 15-20% of the rate of active ATP-dependent Na-K exchange.2. We have studied activation of this Rb-Rb exchange by ATP at fixed phosphate concentrations and by phosphate at fixed ATP concentrations. It is found for both ATP and phosphate that with low concentrations of the fixed ligand an increase in concentration of the complementary ligand produces first stimulation and then inhibition of Rb-Rb exchange. At high concentrations of the fixed ligand the complementary ligand shows only saturation behaviour.3. The pattern of activation and of inhibition by ATP and by phosphate is affected by the Rb(0) concentration in the exterior medium, in that higher concentrations of Rb(0) counteract inhibitory effects of high concentrations of ATP and phosphate.4. (ATP+phosphate)-stimulated Rb-Rb exchange is activated by Rb(0) in the exterior medium along a sigmoid curve. An increase of Rb(i) within the vesicles, which raises the maximal velocity of Rb-Rb exchange, is accompanied by a smaller increase in the Rb(0) concentration required for half-maximal stimulation of the Rb-Rb exchange.5. The data are interpreted in terms of a model similar to those proposed by Karlish & Stein (1982a,b), but extended to include simultaneous effects of ATP and phosphate. Inhibitions by high concentration of ATP or phosphate arise as a result of stabilization of E(1) ATP or E(2)-P forms respectively, in the presence of low concentrations of the complementary ligand. With high concentrations of the fixed ligand, saturation behaviour of the varying ligand is observed because the occluded Rb forms become the dominant transport intermediates. The occluded Rb forms bind both ATP and phosphate weakly and independently. The effects of ATP together with phosphate are accounted for by a simple combination of their separate effects on the Rb-Rb exchange.6. We suggest that the functional role of the occluded Rb form E(2) (Rb)(occ) in active transport is to minimize passive cation leaks through the system and allow control of the direction of cation movements by binding of physiological ligands such as ATP or phosphate.

Electrophoretic control of reconstituted adenine nucleotide translocation.

The initial velocity of adenine nucleotide exchange catalyzed by the reconstituted ADP-ATP carrier from beef heart mitochondria was measured under the influence of membrane potential and with different nucleotide distributions between the internal liposomal and the external buffer volume. Both Vmax and Km of adenine nucleotide uptake not only changed due to the applied potential but also depended on the respective nucleotide distribution. The rate equations for the ADP-ATP exchange under the various conditions were derived. These equations were simplified by assuming two alternative situations; either (a) af affinity type model, where the membrane potential influences only the affinity of the adenine nucleotide carrier toward ATP and ADP, or (b) a velocity type or distribution model, where the membrane potential modulates the rate constants of the ADP-ATP exchange. On the basis of several simplifications in the reconstituted system, the rate equations could be solved and the rate constants and dissociation constants of the exchange in the "energized" and in the "deenergized" state could be calculated. These values were used to derive prediction tables for normalized exchange rates under different nucleotide distributions, which were then compared with the experimental data. Only the exchange rates predicted by the velocity-type model agreed with the measured values. On the basis of this model a definite asymmetry caused by the membrane potential could be seen. Whereas this asymmetry is not very pronounced in the case of carrier-ADP complexes, about 40 times more ATP-loaded binding sites face the outside of the vesicles in the energized state.

Efflux du 36Cl et distribution du Cl dans le muscle papillaire du lapin, effet de l'ouabaïne

The 36Cl efflux "in vivo" was measured in the rabbit papillary muscle to determine the Cl distribution in the muscle and to evaluate the effect of ouabain on this parameter. The results obtained for the 36Cl efflux are analyzed using either a two-compartment model or a model including diffusion in the extracellular space in series with one compartment. The Cl exchange with 36Cl, [Cl]i (intracellular Cl content which has participated in exchange, Cl in equilibrium with 36Cl) is computed from the exponential terms of the models. A time exposure of 40 and 80 min to the 36Cl-containing solution led to the same exchange Cl content: 20.5 and 23.9 mmol/kg cells. Addition of ouabain (10(-6) M) slightly increased the rate constant of the cellular compartment, but did not influence the [Cl]i. In the presence of ouabain (10(-6) M), there was a significant increase in the efflux component with a rapid rate constant. These results can be interpreted as follows: the Cl intracellular concentration is not affected by ouabain; thus, the increase in total Cl content induced in the papillary muscle by ouabain is located in a compartment having a very rapid exchange velocity with the extracellular medium.

A heparin-sensitive nuclear protein kinase. Purification, properties, and increased activity in rat hepatoma relative to liver.

A cyclic-nucleotide independent heparin-sensitive nuclear protein kinase (NII) from the Morris hepatoma 3924A has been purified by a combination of ion exchange and affinity chromatographic procedures and velocity gradient centrifugation. The purified kinase had a molecular weight of 140,000 as determined by gel filtration. Two polypeptides (Mr = 42,000 and 25,600) were present in the purified preparation in approximately equimolar concentrations. The protein kinase employed Mg2+ and Co2+ as divalent ion and preferred the nonhistone proteins, casein or phosvitin, as protein acceptors. In the presence of Mg2+, it utilized both ATP and GTP as substrates and transferred the terminal nucleotide phosphate to serine and threonine residues of the protein acceptor. Phosphorylation of casein was stimulated by polyamines, particularly spermine. This polyamine preferentially enhanced phosphate transfer to threonine. The enzyme was inhibited by several compounds including heparin, the o-n-octyloxime of rifamycin (AF/013), 3'-dATP, o-phenanthroline, polynucleotides, and ADP. Of these inhibitors, heparin was the most potent and completely abolished kinase activity at a concentration of 0.1 micrograms/ml. The kinase could be autophosphorylated by incubation with Mg2+ and [gamma-32P]ATP; under these conditions phosphorylation was confined to the polypeptide of Mr = 24,600 and was completely inhibited by heparin. Based on the unique properties of NII protein kinase (ability to use GTP, stimulation by spermine, sensitivity to heparin), a selective assay was developed which could measure NII activity in the presence of other nuclear kinases. Under the optimal assay conditions, the nuclear extract of hepatoma 3924A was found to contain at least five times more NII kinase activity than that of normal adult liver. Analysis of extensively purified preparations from the two sources confirmed these results. After purification 11 times more NII protein kinase activity was obtained from hepatoma 3924A than from liver. Although hepatoma and liver protein kinases exhibited many common properties, they displayed distinct nucleotide saturation kinetics. The apparent Km for ATP was 10 microM for hepatoma protein kinase and 24 microM for the liver enzyme.

Studies on syntheses and permeabilities of special polymer membranes. 40. Formation conditions of finger-like cavities of cellulose nitrate membranes

The permeation characteristics for polymer aqueous solution and asymmetric structure of cellulose nitrate membranes, in particular the finger-like cavity in the back sponge layer of these membranes, were investigated by changing the preparation conditions of the membranes— the casting solvent, evaporation period, and gelation medium. The formation of the finger-like cavity was dependent on absorption of a water molecule into the casting mixture from the atmosphere during the solvent evaporation process and the exchange velocity between the casting solvent and the gelation medium. The mechanism and conditions for the formation of a finger-like cavity in cellulose nitrate membranes were discussed.

The absorption and evaporation of tritiated water vapor by soil and grassland

The absorption and loss of tritiated water (HTO) vapor at bare soil and grass surfaces were studied in laboratory and field experiments. The exchange involves turbulent mixing in the air and diffusion within the soil. In short exposures it was found that uptake by moist soil was controlled by atmospheric mixing and was described by an exchange velocity of about 1 cm s−1. The exchange velocity was a little smaller for air-dried soil and grass surfaces. For exposure times exceeding a few minutes re-evaporation reduced the rate of net uptake, but the total amount deposited continued to increase as the HTO diffused deeper into the surface. The diffusion coefficient for HTO in soil was investigated in the laboratory and a simple equation was derived to predict the effective diffusion coefficient. Tritiated water, absorbed during a brief exposure, evaporated during several weeks. Its behavior was described by the diffusion equation, but unexplained discrepancies were found in apparent diffusion coefficients in field conditions. Rain washed the activity into the soil and impeded evaporation. Most of the HTO vapor interacts with the surface within two or three days following a low level release. The effect of the surface exchange on the distribution of dose following a release of HTO vapor may be large, but will depend on the weather over a period of weeks and is difficult to foresee.

Stabilization of a Round Jet Flame with a Recirculation Zone in Parallel Air Flow : Part II. Mass Exchange Between the Recirculation Zone and the Outer Flows

Both mass exchange processed between the recirculation zone and the outer flows (mixture and parallel air flow) have been studied regarding the mixing process as complete mixing and applying the results in our previous report of this study to the exchange processes. Each mass exchange and exchange velocity could be obtained from flow rates and the residence time. Measurements of the residence time for cold flow using the tracer method have been made in different burners of 8 mm i.d. with rims of thickness between 3 and 7 mm, and a successful dimensionless group could be found for the residence time. The characteristics of each mass exchange are discussed in terms of these results.

The Balgzand (Dutch Wadden Sea) tidal flats as a source of soluble silicate

The huge numbers of molluscs, worms and bacteria found in the sheltered tidal flats of the Dutch Wadden Sea, decompose large amounts of organic matter. In this process nutrients incorporated in the particulate organic matter are transferred to the dissolved state. The importance of this process for nutrient budgets was first demonstrated by POSTMA (1954) and later by various authors with emphasis on tidal watersheds and sheltered bays (see Neth. J. Sea Res., 8 (2/3). 1974). The nutrient budgets of the Balgzand tidal flats, as a typical example of a sheltered bay, have been studied during one tidal period by TIJSSEN and VAN BENNEKOM (1976) and recently for a longer period in a cooperative project by the “Studiedienst Hoorn” of “Rijkswaterstaat” (DE BOER, 1978) and the Netherlands Institute for Sea Research (MANUELS, 1978). A qualitative measure for the high intensity of mineralization are the high concentrations of nutrients in the water on the Balgzand, compared to those in the Marsdiep (Table I). Simple box models can be used to derive the intensity of nutrient production from the concentration differences in which also the water depth and the exchange velocity of the water with adjacent areas contribute. As a first approximation all mineralization is thought to be situated in the surface sediment (VAN BENNEKOM et al., 1974) and the characteristics parameter becomes the nutrient production per m2 per day. For reactive silicate this parameter shows a pronounced seasonal cycle. In January, February and Marchin situ production is hardly detectable while in July and August 500 mg SiO2 m−2d−1 is found. For comparison, weathering of soil by rain water gives 4–30 mg SiO2.m−2d−1 with only slight seasonal variations. The difference is at least partially explained by assuming a different source: diatom frustules in the case of the Balgzand and silicate minerals in the case of normal weathering. The scarce data available indicate that the seasonal cycles of in situ production of phosphate, nitrate and ammonia on the Balgzand are less pronounced than for reactive silicate. The picture is further complicated because ammonia is always produced, but sometimes nitrate is consumed, apparently by denitrification. The nutrient ratios change during the year (Table II). Especially in summer the contribution of silicate is relatively large. This is in marked contrast with the nutrient ratios in the coastal sea water where during the summer the amount of silicate is relatively low. The nutrient ratios are probably an important factor in the seasonal and regional species composition of the phytoplankton.

Nucleotide polymerases in the developing avian erythrocyte.

Avian erythroid cells were separated into five developmental stages by sedimentation on discontinuous isotonic albumin gradients. Solubilized enzyme activities from whole cells were partially purified and characterized by ion exchange and ion filtration chromatography and velocity sedimenttation analysis. Three nucleotide polymerase types were investigated: (a) DNA-dependent RNA polymerases; (b) RNA-dependent terminal ribonucleotidyltransferases, and (c) DNA-dependent DNA polymerases. The two characteristic forms of eucaryotic DNA-dependent RNA polymerases, polymerase I (nucleolar) and polymerase II (nucleoplasmic), were identified. Polymerase III was only marginally detectable even in the earliest developmental populations. At least two species of RNA-dependent terminal ribosyltransferases were present. One apparently was the poly(A) polymerase observed in other systems. The other terminal transferase was present in two chromatographic forms, required an RNA primer, and used UTP and/or CTP as particularly efficient substrates. Three DNA polymerase activities were resolved, two of which were characteristic of the alpha and beta DNA polymerases described in other eucaryotic systems. The third polymerase was not the gamma polymerase but a separate entity. Poly(dC)-dependent RNA polymerase activity, associated with the alpha polymerase, was relatively enriched in the third DNA polymerase species. The activity levels of the nucleotide polymerases were monitored as a function of red cell maturation. Characteristic declining patterns of activity were obtained for each enzyme which correlate well with the synthetic rates of their in vivo products where these are known. These results correlate well with the synthetic rates of their in vivo products where these are known. These results are consistent with the postulate that the general transcriptive and replicative control processes operating during development may involve changes in the level of the requisite polymerases.