Inhibition of phosphatase activity by dissolved humic substances and hydrolytic reactivation by natural ultraviolet light

1. Phosphatases released extracellularly by aquatic micro-organisms often complex with humic compounds that are released from decomposing tissues of plants and imported in dissolved and colloidal forms to lakes and rivers. 2. Dissolved humic substances from several natural sources formed complexes with phosphatases of bacterial and algal origin and reduced hydrolytic activity by non-competitive inhibition. Restoration of the hydrolytic enzyme activities from the humic substances–enzyme complexes increased progressively over time when exposed experimentally to natural and artificial ultraviolet (UV) irradiance. 3. Greater phosphatase restoration occurred from humic acid–phosphatase complexes when humic acids were extracted from dissolved organic matter (DOM) of mixed natural plant sources, than when humic acids were isolated from a decomposing single plant species. 4. The data support a previously suggested hypothesis that phosphatases and other enzymes in aquatic ecosystems can complex with humic substances that dominate the DOM pool. These humic substances–enzyme complexes, in which the enzyme is temporarily inactivated, can be transported with water movements and displaced to other sites within the ecosystem. Upon exposure to UV irradiance in the photic zone, functional enzymes can be released. The potential for inactivation and storage of enzyme activity, relocation within the ecosystem, and subsequent reactivation holds important implications for regulation of nutrient cycling in fresh waters.     

UV-sensitive P compounds: release mechanism, seasonal fluctuation and inhibitory effects on alkaline phosphatase activity in a shallow Chinese freshwater lake (Donghu Lake)

Filtrable phosphorus compounds in a shallow Chinese freshwater lake (Donghu Lake) were fractionated by Sephadex G-25 gel-filtration chromatography. Some portions of those compounds released soluble reactive phosphorus upon irradiation with low dose ultraviolet light. Catalase and a hydroxyl radical scavenger (mannitol) markedly prevented photosensitive phosphorus release. The observed effects may be explained by the action of oxidizing reagents such as hydroxyl radicals, produced in photochemical reactions between UV irradiation and humic substances in the water. There was a strong seasonality in UV-sensitive P (UVSP) release. Michaels constants (K _m) of total alkaline phosphatase in the lake water showed a direct positive relation to UVSP Plot of K _m against the UVSP/phosphomonoester ratio reveals a strong relationship between the two variables. These results suggest that in some situations UVSP may be a competitive inhibitor of alkaline phosphatase activity in the lake. The competitive inhibition of fractionated UVSP on alkaline phosphatase reagent (Sigma) apparently supports this hypothesis.     

Extracellular enzyme-clay mineral complexes: Enzyme adsorption, alteration of enzyme activity, and protection from photodegradation

Enzymes released extracellularly by micro-organisms have major functions in nutrient acquisition and organic matter degradation. Clay particles, common in many surface waters, can modify enzyme activity. Clay minerals are known to form aggregates with organic molecules, and the formation of enzyme-clay complexes could alter the level of activity. Montmorillonite clay and clay extracted from Elledge Lake (Tuscaloosa, Alabama) basin soil were combined with alkaline phosphatase, glucosidase, protease, and xylosidase solutions to assess adsorption and the effect of this adsorption on enzyme activity. Adsorption to Elledge Lake basin clay decreased alkaline phosphatase activity, and adsorption to montmorillonite was observed for all four enzymes with reductions in enzyme activities. Adsorption of substrate onto clay surfaces resulted in a concentration effect and increased enzyme activity associated with the particles. When enzyme-clay complexes were exposed to natural sunlight there was a decrease in enzyme activity, but this decrease was usually not significantly different from the adsorption only treatment. The formation of enzyme-clay complexes may serve to protect the enzymes from natural in situ photodegradation. The results indicate the complex interactive effects adsorption of enzymes to clay particles can have on the availability and capability of hydrolysis – reduction of enzyme reactivity, storage attached to clay particles with changes in transport and distribution, and protection from photodegradation.     

Effect of cell contact on regionalization of mouse embryos

Cytochemical demonstrations of 5'-nucleotidase and alkaline phosphatase reveal the activity of these enzymes on regions of cell apposition from the late four-cell stage onward. These enzyme activities also appear on regions of artificial cell contact between aggregated embryos having more than four cells. Cytochemistry of single two-cell embryos does not reveal 5'-nucleotidase nor alkaline phosphatase activity, however, these enzyme activities appear at both the artificial and natural contacts in chimaeras of two two-cell embryos. We interpret these results as meaning: (1) that cell contact causes the regionalization of 5'-nucleotidase and alkaline phosphatase activity on the cell surface, (2) that these enzyme activities can be induced or enhanced by contact between two two-cell embryos, (3) that a signal is transmitted from the artificial to the natural contact.     

Similarities between alkaline phosphatase and Ca2+ ATPase activities in HeLa cells

Parallel changes in the enzyme activities of CA2+ATPase and alkaline phosphatase were observed in HeLa cells. Both enzymes were inhibited to a similar degree by L-phenylalanine, L-tryptophan, and L-leucine, while being relatively resistant to L-homoarginine. Exposure to heat (56 degrees C, 60 degrees C, and 65 degrees C) resulted in a loss of both enzyme activities. Both alkaline phosphatase and Ca2+ ATPase, when treated with EGTA, required Ca2+ for the restoration of activity. Cells grown in the presence of agents that affect alkaline phosphatase (dexamethasone, butyric acid, and hyperosmolar NaCl) showed similar changes in the activities of both enzymes.     

Effects of controlled exposure of L cells to bromodeoxyuridine: II. Turnover rates and activity profiles during cell cycle of bromodeoxyuridine-sensitive and -resistant enzymes

Fluorodeoxyuridine (FUdR)-synchronized mouse L cells were allowed to incorporate 5-bromodeoxyuridine (BUdR) at restricted intervals in the S phase and the effects of the selective incorporation of BUdR in DNA on the activities of seven randomly chosen enzymes (five dehydrogenases and two phosphatases) were analysed. Reductions to 56.9 and 83.3 % of the control levels were noted for glucose-6-phosphate dehydrogenase (G6PD) and alcohol dehydrogenase (ADH) activities respectively, when cells were exposed to BUdR during the 1st h of S. Acid phosphatase (AcP) activity was reduced to 81.9% of the control level following exposure to the analogue during the 3rd h of S. Exposure of cells to BUdR for the entire S period failed to increase the magnitude of the reductions in activity for any of these three enzymes. Alternately, when cells were allowed to synthesize DNA in the presence of thymidine for the 1st h of S and the remainder in the presence of BUdR, the activities of G6PD and ADH were comparable to those found in untreated cells. Exposure of cells to thymidine for the 3rd h of S, combined with exposure to BUdR for the preceding and subsequent hours of S, provided complete protection against the BUdR-mediated reduction in AcP activity. The activities of lactate dehydrogenase (LDH), 6-phosphogluconate dehydrogenase (6pGD), isocitrate dehydrogenase (IDH) and alkaline phosphatase (A1P) were found to be insensitive to treatment with BUdR, even when the period of analogue exposure encompassed the entire S period.Additional investigations carried out with G6PD for characterization of the nature of the BUdR effects suggest that the BUdR-mediated reductions in enzyme activities are not caused by the increased rates of degradation of the enzymes, formation of enzyme inhibitors or by the disproportionate replication of A-T base pairs during BUdR treatment. The alterations of enzyme activities appear to result from decreased rates of synthesis of enzymes in BUdR-treated cells. The results of the present study clearly suggest that pulse labelling of cells with BUdR at various intervals of the S phase may provide a useful approach for determining temporal localization of replication time of DNA segments that are critical for the synthesis or regulation of specific gene products.     

Protection against rotavirus diarrhoea in mice by trypsin inhibitor

To investigate the role of soyabean trypsin inhibitor (TI) during rotavirus (RV) diarrhoea, changes in enzyme activities of six relevant mucosal enzymes (lactase, sucrase, maltase, trehalase, glucoamylase and alkaline phosphatase) were assayed following inoculation of suckling mice with EB rotavirus (serotype 3) along with the TI and compared with the age-matched healthy control mice. The animals were divided into three groups i.e. group 1 (controls), group 2 (RV inoculated) and group 3 (RV + TI inoculated and sacrificed under light anaesthesia on 0, 1, 3, 5, 7 and 10 day post inoculation (dpi). Then intestines were excised and divided into two parts (jejunum and ileum). They were separately homogenized in 0.9% cold normal saline and activities of mucosal enzyme were measured. Alkaline phosphatase and disaccharidases were found to be decreased significantly in RV inoculated animals in both the anatomical portions of small intestine of mice. These enzyme levels were restored with the administration of TI i.e. in group 3 and became comparable to the controls in both intestinal portions. These studies suggest that activity of intestinal enzymes which are important in digestive absorptive functions of small intestine were restored with the addition of TI whengiven to infant mice showing its protective efficacy during rotavirus infection.     

Differences in phosphatidate hydrolytic activity of human alkaline phosphatase isozymes

Hydrolytic activities of human alkaline phosphatase isozymes were investigated using phosphatidases with various fatty acyl chains (egg phosphatidate and dioleoyl, distearoyl, dipalmitoyl, dimyristoyl and dilauroyl phosphatidates). In the presence of sodium deoxycholate, purified human placental and intestinal alkaline phosphatases hydrolyzed all the phosphatidates examined. The hydrolytic activity was maximal in the presence of 10 g/l sodium deoxycholate. Of the phosphatidates, dilauroyl phosphatidate was the best substrate. Using the same unit of the enzyme, the phosphatidate hydrolytic activity of placental alkaline phosphatase was 2- to 3-times higher than that of the intestinal enzyme. In contrast, liver alkaline phosphatase did not hydrolyze phosphatidates with long fatty acyl chains (C16-18) even in the presence of sodium deoxycholate. The liver enzyme hydrolyzed dimyristoyl and dilauroyl phosphatidates very slowly. These results show that the phosphatidates with long fatty acyl chains were useful to differentiate placental and intestinal alkaline phosphatases from the liver enzyme, and suggest that the former enzymes play a different physiological role from the liver enzyme.     

Influence of Algal Photosynthesis on Biofilm Bacterial Production and Associated Glucosidase and Xylosidase Activities

Natural photosynthetic biofilms were incubated under light (100 mmol m-2 s-1) and dark conditions to elucidate the impact of photosynthesis on bacterial production, abundance, biovolume, biomass, and enzyme activities over 24 h. Use of organic carbon-free media limited carbon sources to algal photosynthesis and possibly the polysaccharides of the biofilm matrix. Bacterial production of biofilm communities was significantly higher in light incubations (p <0.001). The greatest differences in production rates between light and dark incubations occurred between 8 and 24 h. Biomass-specific a- and b-glucosidase and b-xylosidase activities were stimulated by photosynthesis, with significantly greater activities occurring at hours 16 and 24 in the light treatment (p <0.01). The results indicate that algal photosynthesis can have a significant impact on bacterial productivity, biomass, biovolume, and enzyme production over longer time periods at low photon flux densities (?100 mmol m-2 s-1).     

Intracellular localization of phosphodiesterase induced by cyclic adenosine 3',5'-monophosphate in Dictyostelium discoideum

The intracellular distribution of phosphodiesterase [EC 3.1.4.17] induced by cyclic adenosine 3',5'-monophosphate (cAMP) in Dictyostelium discoideum was studied. When cAMP-treated cells were homogenized and fractionated according to the method of de Duve et al. ((1955) Biochem, J. 60, 604), the specific activity of phosphodiesterase was highest in the light mitochondrial fraction. Peaks of specific activities of alkaline phosphatase (marker enzyme of membrane) and catalase (marker enzyme of peroxisomes) also appeared in the same fraction as phosphodiesterase. However, after centrifugation of the light mitochondrial fraction in a sucrose density gradient, the activity of phosphodiesterase was clearly separated with that of catalase (density 1.19 g/ml) and showed three peaks at lower density (1.10, 1.13, 1.17 g/ml) with good reproducibility. Some parts (1.13, 1.17 g/ml) of the activity in the gradient overlapped with alkaline phosphatase activity, but in the density fraction of 1.10 g/ml the activity of alkaline phosphatase was hardly detectable. When the light mitochondrial fraction was treated with Emulgen 108, or sonicated, phosphodiesterase was more easily solubilized than alkaline phosphatase and catalase, and was found in supernate after centrifugation at 20,000 X g for 30 min. In order to distinguish the locations of the three enzymes, the supernatant of the light mitochondrial fraction treated with Emulgen 108 was subjected to charge shift electrophoresis. The electrophoretic mobilities of phosphodiesterase and catalase were unaffected by ionic detergent. However, alkaline phosphatase shifted towards the anode in the presence of anionic detergent (sodium deoxycholate), and shifted towards the cathode in cationic detergent (cetyltrimethylammonium bromide), relative to nonionic detergent (Emulgen 108) alone. Thus, some part of the phosphodiesterase induced by cAMP may be associated with the plasma membrane, but the remainder is localized in some kind of intracellular particle of lower density. Moreover, the association with the membrane or particle is more easily dissociated than that of alkaline phosphatase, and the liberated phosphodiesterase is rather hydrophilic.     

Effect of starvation on tissue and serum gluconeogenic enzymes, alkaline phosphatase and tissue glycogen in the freshwater catfish, Heteropneustes fossilis (Bloch).

The influence of starvation has been studied on tissue and serum G-6Pase F-D-Pase and alkaline phosphatase activities and on the muscle and liver glycogen content of the freshwater catfish H. fossilis (Bloch). A marked increase in G-6Pase and F-D-Pase activities and a fall in the muscle and liver glycogen content recorded during 40 day starvation. The rise in gluconeogenic enzymes during starvation may be due to glucocorticoid stimulation. Alkaline phosphatase activity was found to decline markedly during starvation. The decline in enzyme activity is attributed to some factors like a fall in the rate of synthesis caused by lowered metabolic demands and to electrolyte imbalance caused by tissue overhydration. The fall in glycogen content may be related to the starved condition of the fish. Elevation in glycogen content and alkaline phosphatase activity and a fall in gluconeogenic enzymes were noted when feeding had been resumed.     

Acid and alkaline phosphatases activities in vascular smooth muscle: species differences and subcellular distribution

1. Acid and alkaline phosphatase activities were studied in rat and dog aortic muscle using p-nitrophenyl phosphate (p-NPP) as the substrate. Alkaline phosphatase activity was quite comparable to acid phosphatase activity in rat aortic microsomes as well as further purified plasma membranes, but considerably lower than acid phosphatase activity in dog aortic membranes. 2. Subcellular distribution of acid and alkaline phosphatase activities in these vascular muscles indicated that alkaline phosphatases and a large portion of acid phosphatase activities were primarily associated with plasma membranes and the distribution of acid phosphatase showed little resemblance to that of N-acetyl-beta-glucosaminidase, a lysosomal marker enzyme. 3. The rat aortic plasmalemmal acid and alkaline phosphatase activities responded very differently to magnesium, fluoride, vanadate and EDTA. The alkaline phosphatase was more susceptible to heat inactivation than acid phosphatase. 4. These results suggest that these two phosphatases are likely to be two different enzymes in the smooth muscle plasma membranes. The implication of the present findings is discussed in relation to the alteration of these phosphatases in hypertensive vascular diseases.     

The relationship of alkaline phosphatase, CaATPase, and phytase

Alkaline phosphatase, highly purified from bovine intestinal mucosa, has significant hydrolytic activity against phytate and CaATP. Phytase and CaATPase activities require quite different assay conditions than those which are optimal for conventional alkaline phosphatase substrates such as 4-nitrophenyl phosphate. We have used affinity chromatography and antibody recognition to demonstrate that the phytase and CaATPase activities are not due to contaminating enzymes, but are intrinsic activities of intestinal alkaline phosphatase. All of the phytase and CaATPase activities present in crude extracts of bovine intestinal mucosa can be accounted for by alkaline phosphatase. Apparently neither phytase nor CaATPase exist in this tissue as independent enzymes. Specific substrates which require assay conditions quite different from the conventional 4-nitrophenyl phosphate substrate may account for the physiological function of "alkaline phosphatase."     

Regulation of alkaline phosphatase activity in rat hepatoma cells. Effects of serum proteins, cycloheximide, actinomycin D, chloroquine, dinitrophenol and potassium cyanide

Alkaline phosphatase activity in rat hepatoma cells (R-Y121B) cultured in a monolayer at 0.5% serum was enhanced by serum, bovine serum albumin, casein and gamma-globulin, but ovalbumin, polyvinylpyrrolidone, dexamethasone, insulin and dibutyrylcyclic AMP showed little effect on alkaline phosphatase activity. In addition, cycloheximide, actinomycin D, chloroquine, dinitrophenol and potassium cyanide also increased the enzyme activity, although the incorporation of [14C]leucine into cellular proteins was almost completely inhibited in the presence of these cytotoxic substances. When R-Y121B cell homogenates were incubated at 37 degrees C, alkaline phosphatase activity increased in a pH-dependent manner: the maximal increase was observed at pH 7.1. The magnitudes of the increase differed among cell homogenates and a 4- to 10-fold increase was observed. Alkaline phosphatase in R-Y121B cells was apparently heat-stable, but that in the cells obtained from various treatments was heat labile and the latter activity decreased to less than 50% of the initial activity after 15 min of incubation at 56 degrees C. Alkaline phosphatase in the control and also in the treated cells was more sensitive to L-homoarginine than L-phenylalanine. The Lineweaver-Burk plot showed that the increases in the enzyme activity were accompanied by changes not only in V but also in Km for alkaline phosphatase reaction. Finally, it has been suggested that the increases in alkaline phosphatase activity under various conditions are due to the conversion of the molecule with a low enzyme activity to the molecule with a high enzyme activity in R-Y121B cells.     

桃小食心虫幼虫越冬前后对几种杀虫剂敏感性的差异

用药液浸渍法测定了桃小食心虫幼虫越冬前和越冬后对三唑磷、辛硫磷、马拉硫磷、毒死蜱、高效氯氟氰菊酯和阿维菌素等杀虫剂的敏感性差异.结果表明:越冬后幼虫对上述药剂的敏感性分别是越冬前幼虫的34.50、16.71、3.89、3.28、5.90和2.73倍.幼虫越冬后体内能源物质蛋白质、糖元和脂肪含量分别比越冬前降低17.10%、41.76%和30.08%;羧酸酯酶、酸性磷酸酯酶、碱性磷酸酯酶及谷胱甘肽-S-转移酶的活力分别比越冬前降低62.36%、53.47%、76.19%和80.60%;超氧化物歧化酶、过氧化氢酶、过氧化物酶等保护酶活力比越冬前分别降低18.77%、14.16%和64.02%;而幼虫体内多种农药的靶标酶乙酰胆碱酯酶活力的变化则相反,该酶在越冬后幼虫体内的活力是越冬前的1.41倍.表明越冬后幼虫对药剂敏感性的提高与体内能源物质含量、代谢酶、保护酶和靶标酶的活力变化有关.     

Synthesis and secretion of phosphatases by endophytic isolates of Colletotrichum musae grown under conditions of nutritional starvation

Even though fungal phosphatases are widely used to study ambient-regulated gene expression, little is known about these enzymes in the agriculturally important genus Colletotrichum. We have therefore identified several phosphatase activities in endophytic isolates of Colletotrichum musae grown under conditions of nutritional sufficiency or starvation for sources of phosphorus (P), nitrogen (N), carbon (C), and sulphur (S). These enzyme forms could be distinguished by substrate specificity, optimum pH, activation and inhibition by some substances, response to nutritional starvation, and pattern of migration in native gel electrophoresis. At least four individual phosphatase activities were identified under the growth conditions employed. A pH 5.0 acid phosphatase and an Mg(2+)-dependent pH 7.5 phosphodiesterase were expressed under all growth conditions at constant rates. Under conditions of P-starvation, derepression of a major pH 6.0-acid phosphatase was observed in cell-free extracts and the culture medium. A synthesis of alkaline phosphatase activities followed a more distinct pattern. Under conditions of nutritional sufficiency of P- or N-starvation, only a single intracellular enzyme form (optimum pH 10) was observed, which was resolved as a single electrophoretic activity band. However, in media lacking C or S sources additional alkaline phosphatase forms were derepressed with a concomitant increase in the overall enzyme activity level measured at pH 10. To our knowledge, this report represents the most detailed study of phosphatases in Colletotrichum and the first partial characterization of the phosphatase system in an endophytic fungus.     

Effects of the Addition of Humic Substances on Soil Protease Activities in Andosols in the Presence of Cadmium

Cadmium extraction, sorption, and immobilization seem to be the effective mechanisms in detoxification of Cd-contaminated soil. Humic substances present in soils may play an important role both in controlling the negative effects of pollution with Cd and in stabilizing soil enzymes. In this context, we have compared the effects of humic substances on soil protease activities in the presence and absence of Cd in forest and cultivated field soil samples. The samples were taken from surface soils of Andosols in a single upland area of the Kanto district in Japan. Humic substances extracted from the two soils showed differences in elemental composition, the degree of condensation of aromatic groups, and the proportions of major functional groups. Compared with the control soil samples, those with added humic substances showed a significant increase in protease activities, even in the presence of Cd (10 and 50 mg Cd kg^?1 soil). However, the addition of Cd decreased the protease activities, protein contents, and soil pH in both soil samples at each of the two levels of humic substance fortification (+5% and +10%). Moreover, protease activities showed significant negative correlation with exchangeable Cd, but adding humic substances did not lead to a reduction in either sample. Thus, although the addition of humic substances increased and stabilized protease activities, it did not lead to a clear reversal of enzyme inhibition by Cd. The obtained results indicate that in both soil samples the humic substances used in this study did not have sufficient affinity to adsorb Cd, and the impact on enzyme activities depends on the difference in chemical characteristics of the added organic matter, as suggested by the difference in enhancement of protease activities between forest and cultivated field soil samples.     

A histochemical study about the influence of lytic enzymes on plasma membrane enzyme activities in rat liver and kidney.

1. The effect of lipolytic, glycolytic and proteolytic enzymes on the activities of plasma membrane enzyme activities in rat liver and kidney has been investigated by a pretreatment of tissue sections with the lytic enzymes. 2. The action of the proteolytic enzymes causes a very strong decrease of leucyl-beta-naphthylamidase activity, whereas the activities of ATP-ase, 5'-nucleotidase and alkaline phosphatase show a lesser decrease. This indicates a different membrane anchorage of leucyl-beta-naphthylamidase as compared to that of the phosphatases. 3. Treatment with glycolytic enzymes results in a decrease of 5'-nucleotidase and ATP-ase activity, whereas liver alkaline phosphatase and leucyl-beta-naphthylamidase show an increase in activity. 4. Treatment with phospholipase C gives about the same results. The very strong decrease of 5'-nucleotidase activity indicates a great dependence on phospholipids.     

Thymidine as synchronizing agent. 3. Persistence of cell cycle patterns of phosphatase activities and elevation of nuclease activity during inhibition of DNA synthesis

Synchronous cultures of HeLa cells were obtained by selective detachment of cells in mitosis and fluctuations in enzyme activity were followed during the subsequent cell cycle. The enzymes measured were alkaline and acid phosphatases and a nuclease active on denatured DNA at alkaline pH (alkaline DNase). Each of these enzymes showed a different pattern of activity in the cell cycle, but a temporal relationship to the DNA synthetic phase was apparent in each case. Treatment of the cultures at the beginning of the cell cycle with 15 mM thymidine did not alter the subsequent pattern of fluctuations in activity of alkaline phosphatase or of acid phosphatase, although DNA synthesis was fully inhibited by this treatment. This indicates that the pattern of activity of some enzymes is not linked to DNA replication. On the other hand, the pattern of fluctuations in the activity of alkaline DNase was abolished by thymidine treatment, and elevation of the activity of this enzyme was observed. These results suggest complex and variable relationships between phases of the cell cycle and enzyme activity, and show that inhibition of DNA synthesis is not a suitable procedure for induction of culture synchrony if enzyme activities are to be studied.     

Ion-transporting ATPases and matrix mineralization in cultured osteoblastlike cells

Cultures of osteoblastlike cells obtained from the endosteal surfaces of rabbit long bones formed and mineralized an extracellular matrix when they were supplied daily with medium containing fresh ascorbate. No matrix formed without this supplementation. The matrix mineralized whether or not beta-glycerophosphate, a substrate of alkaline phosphatase, was added to the medium. The ion-transporting ATPase activities of untreated, ascorbate-treated, and ascorbate plus beta-glycerophosphate-treated cells were measured. Ascorbate-treated and ascorbate plus beta-glycerophosphate-treated cells had similar enzyme activities. The activities of the Ca2+-ATPase; Ca2+,Mg2+-ATPase; and alkaline phosphatase in treated cells were elevated over the activities in untreated cells. Na+,K+-ATPase activity was lower in treated than in untreated cells. HCO3--ATPase activity was not changed by treatment. Alkaline phosphatase activity was 20 times higher in freshly isolated osteoblastlike cells than in cells grown to confluence in primary culture. In addition, subculturing further reduced the activity of this osteoblast-marker enzyme. The activities of the ion-transporting ATPases and alkaline phosphatase in second passage cells were similar to the activities of these enzymes in fresh, noncalcifying tissues. Nevertheless, second passage cells retain the ability to mineralize an extracellular matrix, and their ion-transporting ATPase and alkaline phosphatase activities are altered when the cells mineralize a matrix.