The enzymatic preparation of [alpha-(32)P]nucleoside triphosphates, cyclic [32P] AMP, and cyclic [32P] GMP.

A method has been developed for the enzymatic preparation of alpha-(32)P-labeled ribo- and deoxyribonucleoside triphosphates, cyclic [(32)P]AMP, and cyclic [(32)P]GMP of high specific radioactivity and in high yield from (32)Pi. The method also enables the preparation of [gamma-(32)P]ATP, [gamma-(32)P]GTP, [gamma-(32)P]ITP, and [gamma-(32)P]-dATP of very high specific activity and in high yield. The preparation of the various [alpha-(32)P]nucleoside triphosphates relies on the phosphorylation of the respective 3'-nucleoside monophosphates with [gamma-(32)P]ATP by polynucleotide kinase and a subsequent nuclease reaction to form [5'-(32)P]nucleoside monophosphates. The [5'-(32)P]nucleoside monophosphates are then converted enzymatically to the respective triphosphates. All of the reactions leading to the formation of [alpha-(32)P]nucleoside triphosphates are carried out in the same reaction vessel, without intermediate purification steps, by the use of sequential reactions with the respective enzymes. Cyclic [(32)P]AMP and cyclic [(32)P]GMP are also prepared enzymatically from [alpha-(32)P]ATP or [alpha-(32)P]GTP by partially purified preparations of adenylate or guanylate cyclases. With the exception of the cyclases, all enzymes used are commerically available. The specific activity of (32)P-labeled ATP made by this method ranged from 200 to 1000 Ci/mmol for [alpha-(32)P]ATP and from 5800 to 6500 Ci/mmol for [gamma-(32)P]ATP. Minor modifications of the method should permit higher specific activities, especially for the [alpha-(32)P]nucleoside triphosphates. Methods for the use of the [alpha-(32)P]nucleoside phosphates are described for the study of adenylate and guanylate cyclases, cyclic AMP- and cyclic GMP phosphodiesterase, cyclic nucleotide binding proteins, and as precursors for the synthesis of other (32)P-labeled compounds of biological interest. Moreover, the [alpha-(32)P]nucleoside triphosphates prepared by this method should be very useful in studies on nucleic acid structure and metabolism and the [gamma-(32)P]nucleoside triphosphates should be useful in the study of phosphate transfer systems.     

Preparation of [32P]phosphatidylcholine and [32P]lysophosphatidylcholine by using soya beans.

This method describes a procedure that can be carried out easily to obtain large amounts of [32P]phosphatidylcholine and [32P]lysophosphatidylcholine. The method involves germinating soya beans in the presence of [32P]Pi. The yield was 0.58% for [P]phosphatidylcholine and 0.52% for [32P]lysophosphatidylcholine, and the specific radioactivity of both was 10(7) d.p.m./mumol.     

Plasma membrane-associated phosphatase activities hydrolyzing [32P]phosphotyrosyl histones and [32P]phosphatidylinositol phosphate

We describe a procedure of preparing [32P]phosphotyrosyl histones with minimal contamination by 32P-labeled lipids; the latter was usually found to be mixed with the phosphoproteins when the cell membrane-enriched fraction of A-431 cells was used as a source of tyrosine kinase. The phosphatase activities previously found to be associated with the plasma membranes of a human astrocytoma were resolved using purified [32P]phosphotyrosyl histones and [32P]phosphatidylinositol phosphate. In comparison with the phosphotyrosyl protein phosphatase, the phosphatidylinositol phosphate phosphatase activity is more active over a broad range of pH values, and its activity is inhibited by fluoride, zinc chloride, and lower concentrations of vanadate.     

Enzymatic synthesis of [beta-32P]ADP using adenylate kinase and [gamma-32P]ATP

An enzymatic method for the synthesis of [beta-32P]ADP from [gamma-32P]ATP is described. This substrate is required for the assay of ADPase and is not commercially available. The method described results in a preparation of [beta-32P]ADP of high purity with a yield of approximately 40% the theoretical obtainable.     

32P-labeling of bovine tryptophanyl-tRNA synthetase with [32P]pyrophosphate

The covalent derivative of the tryptophanyl-tRNA synthetase obtained under the action of³²PP_i contains one mole of the covalently bound pyrophosphate (or 2 moles of orthophosphate) per mole of dimeric enzyme. Dephosphorylation with alkaline phosphatase causes practically no changes of enzymatic activity although the enzyme looses its ability to bind PP_i.Enzymes tryptophanyl-tRNA synthetase (EC 6.1.1.2), alkaline phosphatase (EC 3.1.3.1), inorganic pyrophosphatase (EC 3.6.1.1)     

Synthesis of [gamma-32P]thiamine triphosphate

We developed a novel chemical synthesis of thiamine triphosphate which allows us to incorporate 32P in the gamma position. The reaction is based on the condensation of [32P]orthophosphoric acid and thiamine diphosphate in the presence of ethyl chloroformate. After purification by two ion-exchange purification steps, the thiamine derivative has a specific radioactivity of 10 Ci/mmol. The average final yield synthesis is about 10%.     

An enzymatic method for [32P]phosphoenolpyruvate synthesis

A convenient method for the enzymatic synthesis of [³²P]phosphoenolpyruvate from [γ-³²P]ATP using partially pufified phosphoenolpyruvate carboxykinase from Escherichia coli is described. The synthesis was shown to convert essentially all the [γ-³²P]ATP to [³²P]phosphoenolpyruvate, which was subsequently separated from residual [γ-³²P]ATP and $\text{[}{}^{32}\text{P}\text{]P}{}_{\mathrm{<mtext>i</mtext>}}$ by chromatography on AG-1-X8-bicarbonate resin.     

The rapid, simple and improved preparation of high specific activity alpha-[32P]dATP and alpha-[32P]ATP.

An improved method is described for the rapid and simple preparation of alpha-[32P]dATP and alpha-[32P]ATP from 32Pi in good yields and with specific activities from 20 - 150 Ci/mmol. The two-step procedure involves the chemical synthesis of the mononucleotide followed by its enzymic conversion to the triphosphate with myokinase (EC 2.7.4.3) and pyruvate kinase (EC 2.7.1.40) in the presence of trace amounts of dATP or ATP to prime the reaction. The two steps are carried out in the same reaction flask and the only purification step required is a step-wise elution from a column of DEAE-cellulose.     

Formation of palmityl-[13'-32P]coenzyme A from [gamma-32P]ATP in mitochondrial extracts of guinea pig liver.

Investigations of the incorporation of ³²P into acyl-coenzyme A (CoA) in incubation mixtures containing a soluble protein preparation derived from mitochondria, [γ-³²P]ATP, and palmityl-CoA have led to the discovery of an enzymatic activity which catalyzes the exchange of palmityl groups between molecules of CoA: CoA¹ + palmityl-CoA ? palmityl-CoA¹ + CoA. The preparation also contains dephospho-CoA kinase and palmityl-CoA thiolester hydrolase activities. The initial detection of the exchange reaction resulted from the formation of [3′-³²P]CoA via the dephospho-CoA kinase reaction with exogenous [γ-³²P]ATP. The described preparation of palmityl-[3′-³²P]CoA and palmityl-[³⁵S]CoA facilitated demonstration of the reversibility of the reaction and ruled out the possibility that the exchange of fragments of the CoA molecule mediated the observed incorporation. The reversible palmityl group exchange does not appear to be catalyzed by a previously described enzyme. None of the possible acyl group acceptors considered in these studies participated in the reaction as efficiently as CoA itself. The possibility is discussed that the exchange reaction may explain reports of an unknown lipid formed by an oligomycin-sensitive mitochondrial ATPase preparation.     

Incorporation of [32P]- and [14C]-ATP intoEscherichia coli isocitrate lyase

InEscherichia coli, isocitrate lyase has been shown to be phosphorylated in vitro by [-³²P]-ATP on histidine residues. This phosphorylation is believed to be necessary for activity of this enzyme. Previous work has shown that treatment of isocitrate lyase with acid phosphatase leads to a decrease in activity as well as a loss of incorporated [³²P]-phosphate in a time-dependent manner. In addition to phosphorylation by [-³²P]ATP, isocitrate lyase has been found to incorporate radioactive label from [-³²P]ATP and from [¹⁴C]ATP. This finding may indicate that more than one type of covalent modification occurs on this enzyme. Isocitrate lyase activity, inE. coli, may be regulated by posttranslational modification in several ways.     

Carrier-free 8-azidoadenosine 5'-[gamma-32P]triphosphate

We found 8-azidoadenosine 5'-diphosphate to be a phosphoryl acceptor in the enzymatic conversion of 1,3-diphosphoglyceric acid to 3-phosphoglycerate. This has allowed us to synthesize in a single-step procedure carrier-free 8-azidoadenosine 5'-[gamma-32P]triphosphate, requiring no further purification of the end product. The synthesized 8-azidoadenosine 5'-[gamma-32P]triphosphate has been characterized and shown to meet all the criteria for a specific photoreactive ATP analogue.     

Studies on the specific activity of [gamma-32P]ATP in adipose and other tissue preparations incubated with medium containing [32P]phosphate

The specific activity of the gamma-32P position of ATP was measured in various tissue preparations by two methods. One employed HPLC and the enzymatic conversion of ATP to glucose 6-phosphate and ADP. The other was based on the phosphorylation of histone by catalytic subunit of cAMP-dependent protein kinase (Hawkins, P.T., Michell, R.H. and Kirk, C.J. (1983) Biochem. J. 210, 717-720). The HPLC method also allowed the incorporation of 32P into the (alpha + beta)-positions of ATP to be determined. In rat epididymal fat-pad pieces and fat-cell preparations the specific activity of [gamma-32P]ATP attained a steady-state value after 1-2 h incubation in medium containing 0.2 mM [32P]phosphate. Addition of insulin or the beta-agonist isoprenaline increased this value by 5-10% within 15 min. Under these conditions the steady-state specific activity of [gamma-32P]ATP was 30-40% of the initial specific activity of the medium [32P]phosphate. However, if allowance was made for the change in medium phosphate specific activity during incubations the equilibration of the gamma-phosphate position of ATP with medium phosphate was greater than 80% in both preparations. The change in medium phosphate specific activity was a combination of the expected equilibration of [32P]phosphate with exchangeable intracellular phosphate pools plus the net release of substantial amounts of tissue phosphate. At external phosphate concentrations of less than 0.6 mM the loss of tissue phosphate to the medium was the major factor in the change in medium phosphate specific activity. It is concluded that little advantage is gained in employing external phosphate concentrations of less than 0.6 mM in experiments concerned with the incorporation of phosphate into proteins and other intracellular constituents. Indeed, a low external phosphate concentration may cause depletion of important intracellular phosphorus-containing components.     

Chemical synthesis of [32P]pyrophosphate with high specific activity

Graphical methods have traditionally been the principal means for estimation of parameters (e.g., affinity constants, cooperativity parameters, and concentrations of receptor sites) in enzymology and ligand-binding problems. The present report provides a review of these methods as well as new results, as applied to three coordinate systems popularly used in ligand-binding studies: $\text{B}\text{F}$ vs [Bound]. $\text{B}\text{F}$ vs [Free], and $\text{B}\text{F}$ vs [Total]. We consider two extremely general models, the statistical mechanical model and the Adair model for equilibrium ligand binding. We also consider a very specialized case of receptor interaction wherein the equilibrium constannt of dissociation is linearly related to receptor occupancy. We collect previously described equations and derive new ones, to enable the user to estimate the parameters of the models in terms of relatively easily measurable graphical characteristics. We have evaluated the performance of these methods in representative cases using Monte Carlo studies. The results indicate the kind of precision and accuracy which can be obtained with typical experimental designs. Depending upon the magnitude of experimental error, the graphical methods can provide dependable values for the binding parameters. However, in general, the results obtained by the graphical methods should be regarded as reasonable initial estimates for further refinement by weighted nonlinear least-squares curve fitting.     

A procedure for the preparation of [32P]phosphatidic acid

The phosphorylation procedure of F. Cramer, W. Rittersdorf, and W. Bohm [(1961) Chem. Ber. 654, 180] using bis(triethylammonium) phosphate and trichloroacetonitrile was shown to be effective in the synthesis of [32P]phosphatidic acid. From diacylglyceride and 0.5 mCi H(3)32PO4, 25-50 microCi of labeled material (sp act = 1 mCi/mumol) can be prepared in 2 h. The product was shown to be radiochemically pure by both TLC and HPLC. L- and DL-[32P]dipalmitoyl phosphatidic acid prepared using this procedure were shown to be hydrolyzed by rat liver microsomes at approximately the same rates.     

Artifactual phosphate binding due to impurities in [32P]orthophosphate

Many commercial preparations of [32P]orthophosphate contain radioactive impurities that interfere with binding and transport studies in biological systems. One type of impurity is micro-particulate whereas another may be pyrophosphate. Methods of removing these impurities from radiolabeled orthophosphate solutions are described.