The phosphotransferase activity of phosphatases. 2. Studies with purified alkaline phosphomonoesterases and some substrate-specific phosphatases

Preparation and structural properties of starch phosphate modified by alkaline phosphatase

In this study, a method for the synthesis of starch phosphate using the transferase properties of alkaline phosphatase was explored. Maize starch was treated with a pyrophosphate solution containing alkaline phosphatase and catalytic ions under pH 8 at 37 °C. The synthesis of starch phosphate was evaluated and compared with untreated and treated starch controls. The phosphorus content of the samples increased up to 8500% with the catalytic ion concentration, whereas the peak viscosity by up to 41.4% decreased. The crystallinity and enthalpy of the phosphorylated samples were reduced by up to 26.8% and 23.3%, respectively; however, no significant was observed by Fourier-transform infrared spectrometer. The roughness of the starch surface and the distribution of elemental phosphorus were observed by scanning electron microscopy and energy dispersive Spectrometry. X-ray photoelectron spectroscopy and time of flight secondary ion mass spectrometry results further indicated the grafting of the phosphate radical.

Key advances in biocatalytic phosphorylations in the last two decades: Biocatalytic syntheses in vitro and biotransformations in vivo (in humans)

Biocatalytic phosphorylation reactions provide several benefits, such as more direct, milder, more selective, and shorter access routes to phosphorylated products. Favorable characteristics of biocatalytic methodologies represent advantages for in vitro as well as for in vivo phosphorylation reactions, leading to important advances in the science of synthesis towards bioactive phosphorylated compounds in various areas. The scope of this review covers key advances of biocatalytic phosphorylation reactions over the last two decades, for biocatalytic syntheses in vitro and for biotransformations in vivo (in humans). From the origins of probiotic life to in vitro synthetic applications and in vivo formation of bioactive pharmaceuticals, the common purpose is to outline the importance, relevance, and underlying connections of biocatalytic phosphorylations of small molecules. Asymmetric phosphorylations attracting increased attention are highlighted. Phosphohydrolases, phosphotransferases, phosphorylases, phosphomutases, and other enzymes involved in phosphorus chemistry provide powerful toolboxes for resource-efficient and selective in vitro biocatalytic syntheses of phosphorylated metabolites, chiral building blocks, pharmaceuticals as well as in vivo enzymatic formation of biologically active forms of pharmaceuticals. Nature's large diversity of phosphoryl-group-transferring enzymes, advanced enzyme and reaction engineering toolboxes make biocatalytic asymmetric phosphorylations using enzymes a powerful and privileged phosphorylation methodology.

Sweet potato acid phosphatase immobilized on glutaraldehyde-activated aminopropyl controlled-pore glass: activation, repeated use and enzyme fatigue

Sweet potato acid phosphatase was covalently coupled with glutaraldehyde to aminopropyl controlled-pore glass, and used as a pre-column enzyme reactor. The immobilized enzyme reactor (IMER) was continuously operated using an automated chromatographic detection system we developed. Functional evaluation of the IMER was carried out by injecting ten samples on the same day at an injection amount of 1.25 nmol (62.5 nmol per ml) using riboflavin sodium phosphate (FMNs) as a substrate, and by prolonged use for ten months. The IMER exhibited decreased activity after repeated use for a total of 3000 samples, but about 75% of its original activity remained. The conversion rate of FMNs to riboflavin by IMER was increased from 89 to 97% by adding citrate, ethylenediaminetetraacetic acid disodium salt, etc., but especially by adding citrate. The increased conversion of FMNs to riboflavin due to the addition of citrate was probably not due to the chelation of heavy metal ions by citrate. We also investigated complex formation of acid phosphatase with the substrate FMNs using surface plasmon resonance to determine the effect of citrate on the processes of association and/or dissociation between the enzyme and substrate. Enzyme fatigue was also observed during the course of prolonged and repeated use.

On-line automated high-performance liquid chromatographic determination of total riboflavin phosphates using immobilized acid phosphatase as a pre-column reactor

An automated chromatographic detection system for the determination of total riboflavin phosphates using immobilized sweet potato acid phosphatase as a pre-column reactor is reported on. An immobilized enzyme reactor, incorporated in the on-line analytical system, hydrolysed riboflavin phosphates to riboflavin, and then lipophilic riboflavin was concentrated at the top of an ODS trap column. Enzymatically hydrolysed riboflavin was back-eluted from the trap column using a mobile phase containing methanol, and then subsequently chromatographed on an ODS analytical column. The effluents were monitored by UV absorption at 280 nm. The calibration graph for total riboflavin phosphates, determined by this method, was linear over the range 0.5-500 nmol/ml, with a correlation coefficient of 0.9999. The detection limit at a signal-to-noise ratio of 3 was 25 pmol/ml. The average conversion rate of riboflavin phosphates to riboflavin was estimated at 97%. The relative standard deviations of the intra- and inter-assay precision were 1.2 and 2.6%, respectively.

Intestinal alkaline phosphatase can transphosphorylate thiamin to thiamin monophosphate during intestinal transport in the rat

Intestinal alkaline phosphatase (IAP) purified from calf intestine and IAP present in the brush border membrane of rat small intestine effectively transphosphorylated thiamin (T) to thiamin monophosphate (TMP) using Na2-beta-glycerophosphate or Na2-creatine phosphate as phosphate donors at pH 8.5. TMP production in the brush border membrane was very small and corresponded to 0.001-0.01 percent of the total inorganic phosphate simultaneously released by the enzyme activity. This reaction, however, could account for TMP formation independently from that much more important due to the hydrolysis of thiamin pyrophosphate during T intestinal absorption.

Relation between intestinal alkaline phosphatase activity and brush border membrane transport of inorganic phosphate, D-glucose, and D-glucose-6-phosphate

In order to evaluate the role of the alkaline phosphatase in intestinal transport processes, we studied the influence of known modulators of the alkaline phosphatase (polyclonal anti-calf AP antibodies, theophylline and zinc ions) on the absorption rate of glucose, inorganic phosphate and glucose liberated from glucose-6-phosphate into calf duodenal brush border membrane vesicles. Our results allow the following conclusions: First a direct involvement of the AP in the Na+-dependent glucose absorption is unlikely. Indeed, theophylline inhibits strongly the AP activity but rather stimulates the glucose uptake; second the AP is indirectly involved in glucose absorption from glucose-6-phosphate, if its enzymatic hydrolysis is the only source of glucose. In that case the Na+-dependent uptake of glucose was completely suppressed either by phosphatase specific antibodies or by theophylline; third the positive correlation found with calf intestinal BBMV between the inhibition of AP by AP antibodies or by theophylline and the decrease of rate of Na+-dependent Pi uptake rate suggests that the enzyme plays some role in the Pi absorption. It appears from the present study that the AP is probably not a carrier protein itself, but its hydrolytic activity might nevertheless be important for intestinal absorption. After hydrolysis of phosphoric esters the alcohol residues and Pi can be supplied to their specific carriers. Furthermore, the high Pi affinity of the enzyme at physiological pH values, could even favour a transient sequestration of phosphate, which then could be transferred to the Pi carrier.

Phosphotransferase activity of human alkaline phosphatases and the role of enzyme Zn2+

Purified isoenzymes of human alkaline phosphatase from placenta, intestine and liver were investigated as catalysts for phosphotransferase activity, using the phosphoacceptors Tris, 2-amino-2-methyl-1-propanol, 2-amino-2-methyl-1,3-propanediol, diethanolamine, 2-(ethylamino)ethanol, ethanolamine, and N-methyl-D-glucamine. All of the compounds supported phosphotransferase catalysis, conforming to saturation kinetics. There was little difference among the isoenzymes with respect to Km values of the acceptors, but the liver form was the most efficient (highest Vmax/Km) in forming phosphoacceptors; it was also the most efficient (highest Vamax/Ka) when the phosphoacceptors were considered as activators. At Vmax the isoenzymes differed little in their support of phosphotransferase activity relative to phosphohydrolysis, although the intestinal enzyme tended to be the poorest. The two best acceptors were diethanolamine, providing the highest phosphotransferase velocity, and 2-(ethylamino)ethanol, having the lowest Km. The phosphoaceptors that bound Zn2+ tightly did not function well in the phosphotransferase reaction, and vice versa. However, temporal assessment of the phosphohydrolytic and phosphotransferase activities during removal of Zn2+ from the enzyme with 1,10-phenanthroline revealed no evidence of a special role for Zn2+ in the latter activity.

Phosphotransferase properties of human erythrocyte phosphoglycolate phosphatase

1. Human erythrocyte phosphoglycolate phosphatase (PGP) (EC 3.1.3.18) shows transferase properties. Using p-nitrophenylphosphate (p-NPP) as substrate, methanol, at a concentration of 4.9 M, was the most efficient phosphate acceptor tested (60% phosphate transfer). 2. The branched alcohols i-propanol and i-butanol accept the phosphate better than the unbranched compounds. The acceptor potency is methanol greater than ethanol greater than i-propanol greater than n-propanol greater than i-butanol greater than n-butanol. 3. The relative transferase activity could be demonstrated to be independent of substrate concentration, pH, and the inhibitory effect of NaF at 2 and 4 mM. 4. PGP shows no transferase activity towards glucose and fructose, and is even inhibited by 250 mM of lactose and lactic acid to 67 and 55%, respectively. 5. Using p-nitrophenyl-[32P]-phosphate (p-NP[32P]P), the direct transfer of phosphate from donor to acceptor could be demonstrated.

Histochemical distribution of enzymes in the small intestine of young milk-fed calves

The histochemical distribution of selected enzymes were examined in the small intestine of 5 about 3-week-old normal calves fed on whole cow’s milk. Alkaline phosphatase and β-D-galactosidase (= lactase) in the epithelial brush border, and non-specific esterase in the cytoplasm showed a strong reaction in the villi of the anterior small intestine and a marked decrease in the posterior regions. Aminopeptidase in the brush border of the villi showed a reverse distribution, with the strongest reaction in the posterior small intestine. Adenosine-triphosphate-splitting enzyme in the epithelial brush border, acid phosphatase and succinate dehydrogenase in the cytoplasm of the epithelial cells gave a relatively uniform reaction in the villi throughout the small intestine. A fluoride-resistant acid phosphatase was demonstrated in the brush border of the villi in the anterior small intestine. The distribution of enzymes demonstrated in this study was generally compatible with the known absorptive functions of the various parts of the small intestine.

Enzymatic properties of the Ca2+-binding glycoprotein isolated from preosseous cartilage

The Ca2+-binding glycoprotein isolated from preosseous cartilage shows also alkaline phosphatase activity. The purification procedure indicates that the enzyme is inhibited in crude extract and conceivably in the intact tissue; the activity may be controlled by the proteoglycans present in the matrix. Other substrates are hydrolyzed by the purified enzyme in addition to p-nitrophenylphosphate; the highest specific activity was measured with ATP and pyrophosphate (PPi) at pH 7.5 and 9.0 Mg2+ induces an activation of ATP and PPi hydrolysis; Ca2+ activates hydrolysis of ATP but inhibits that of PPi. The glycoprotein shows also transphosphorylase activity, L-serine being the best phosphate acceptor. The release or transfer of Pi catalyzed by the glycoprotein can be an important step in calcium phosphate precipitation.

New reaction sequences for the non-oxidative pentose phosphate pathway

1. Reactions leading to the formation of 14C-labelled volatile compounds and compounds volatile under acid conditions were investigated in a system actively synthesizing hexose 6-phosphates from [U-14C]ribose 5-phosphate by reactions catalysed by enzymes prepared from acetone-dried powder of rat liver; no reactions involving 14C-labelled volatile compounds were detected. Similarly the fixation of 14C-labelled volatile compounds into hexose 6-phosphate could not be detected. 2. A complete carbon balance was made for the reactants, intermediates and products of the reactions involved in the conversion of ribose 5-phosphate into hexose 6-phosphate by enzymes of rat liver. Five additional intermediates of pentose 5-phosphate metabolism in liver were detected, namely D-manno-heptulose 7-phosphate, D-altro-heptulose 1,7-bisphosphate, D-glycero-D-ido-octulose 1,8-bisphosphate, D-glycero-D-altro-octulose 1,8-bisphosphate and D-arabinose 5-phosphate. 3. D-Arabinose 5-phosphate was found to be utilized by a rat liver enzyme preparation to produce both hexose 6-phosphate and triose phosphate. 4. D-Arabinose 5-phosphate was reversibly converted into other pentose 5-phosphates. Paper chromatographic and enzymic evidence indicated that the conversion involved an enzyme tentatively named arabinose phosphate 2-epimerase, which catalyses the following reaction: D-arabinose 5-P in equilibrium D-ribose-5-P. 5. A variety of rat tissues also utilized D-arabinose 5-phosphate to produce both hexose 6-phosphate and triose phosphate and at a rate comparable with that obtained with D-ribose 5-phosphate. 6. A new reaction sequence for the non-oxidative pentose phosphate pathway in liver is proposed.

The relations between intestinal alkaline phosphatase and carbohydrates with regard to calcium absorption

The effect of carbohydrates on calcium absorption were studied in situ following the injection of a solution containing CaCl2 (+45Ca) into the ileal loop. The increase in Ca absorption was proportional to the concentration of carbohydrates injected and could be attributed to a progressive increase in the duration of absorption. In the ileal loop, sorbitol was much more effective than L-arabinose at equal concentrations in activating absorption. Such differences in the action of these carbohydrates were also observed in vitro with alkaline phosphatase extracted from the ileum. The transphosphorylating effect of the enzyme was much more pronounced in the case of sorbitol. Since the carbohydrate is a phosphate acceptor, it might influence the duration of absorption by reducing the inhibition exerted by phosphate upon a transfer mechanism which involves phosphatase, another possibility is that carbohydrate could postpone calcium insolubility through the formation of a phosphocarbohydrate complex.

Milk fat globule membranes. Inhibition by sucrose of the alkaline phosphomonoesterase

Sucrose, a widely used agent in the preparation of membranes, inhibited the alkaline phosphomonoesterase of the milk fat globule membrane in both its membrane-bound and detergent-solubilized forms. The inhibition was kinetically competitive and reversible by dialysis. However, its mechanism was more complex than simple competition with substrate because: (a) sucrose induced the appearance of prolonged time-lags in the progress curves of the enzyme; (b) the extent of inhibition and of the time-lags depended on the age of the membrane preparation, the period of pre-exposure of the membranes to sucrose, and the temperature of pre-exposure. On the other hand the acid phosphomonoesterase and the phosphodiesterase activities also present in the membrane preparations were unaffected by the disaccharide.

[Cow's milk alkaline phospharase. II. Subunit structure, metalloproteic nature and kinetic parameters (author's transl)]

Alkaline phosphatase (EC 3.1.3.1) from cow's milk as a dimer comprising two identical or very similar subunits of about 85 000 molecular weight. The enzyme contains 4.9 +/- 0.6 gatoms of zinc per mol of protein. The essential kinetic properties are the same as those of other alkaline phosphatases: variation of pH optimum value, the lack of specificity, increase of Km and V with pH value. The phosphotransferase activity is enlarged, at constant concentration of acceptor, with an increasing concentration of donor. The small size of molecules and the presence of hydroxyls and amino groups increase the percentage of transfer phosphate. The phosphotransferase reaction is better with the D-isomer of serine and the enzyme possesses a more important affinity for the D-phosphoserine.

The inhibition of pig kidney alkaline phosphatase by oxidized or reduced nicotinamide-adenine dinucleotide and related compounds

1. The inhibition of alkaline phosphatase by NAD(+), NADH, adenosine and nicotinamide was studied. 2. All of these substances except NAD(+) act as uncompetitive inhibitors, i.e. double-reciprocal plots are parallel. NAD(+), however, is a ;mixed' inhibitor of alkaline phosphatase and is less potent than NADH. 3. Inhibition studies with pairs of the inhibitors suggest that, in spite of the difference in type of inhibition, NAD(+) and NADH bind to alkaline phosphatase at a common site. Adenosine and nicotinamide also seem to bind at the NAD site and the binding of adenosine is facilitated by nicotinamide, and vice versa. 4. The facilitation may indicate the occurrence of an induced fit for NAD(+) and NADH. Attempts to desensitize alkaline phosphatase to NAD(+) and NADH inhibition by partial denaturation were unsuccessful. 5. The results are discussed in terms of a two-site model in which separate, but interacting, regions exist on the enzyme to accommodate the adenosine and nicotinamide moieties of NAD, and a single-site model in which the adenosine part of the molecule is bound preferentially and this interacts with the nicotinamide fraction. 6. The activity of alkaline phosphatase can be changed fourfold by alteration of the NAD(+)/NADH ratio. This sensitivity to the redox state of the coenzyme could be a means of controlling phosphatase activity.

A chemical relaxation study of human prostatic acid phosphatase

Chemical relaxation methods and a dilution technique were applied to the study of the hydrolysis of p-nitrophenyl phosphate by human prostatic acid phosphatase. Although the reaction mechanism was not elucidated, rate constants and equilibrium constants were obtained for the reaction of enzyme and p-nitrophenol to form a complex. A slow, 2-sec relaxation effect which showed no concentration dependence was observed in various reaction mixtures, including some lacking the substrate and products of the hydrolytic reaction. The conclusion drawn is that there are two forms of the prostatic enzyme, which are normally in equilibrium with each other, but which undergo a relatively slow interconversion when this equilibrium is perturbed. A preliminary calculation indicates that these forms are present in the equilibrium ratio of 2:1.