A rapid radiochemical assay for hypoxanthine-guanine phosphoribosyltransferase

A simple radiochemical method is described for assay of hypoxanthine-guanine phosphoribosyltransferase. ¹⁴C-Hypoxanthine is incubated with enzyme PRPP. The labelled product is precipitated on strips of Whatman No. 1 paper by the addition of lanthanum nitrate. Unreacted substrate is eluted with distilled water. The major advantages of this method are speed, reproducibility, ability to process many samples and low blank values.     

Dephospho-CoA kinase provides a rapid and sensitive radiochemical assay for coenzyme A and its thioesters

A new approach to determine in vivo pools of coenzyme A (CoA) and short chain acyl-CoA thioesters is reported. The metabolites released by extraction with trichloroacetic acid are recovered and quantitatively dephosphorylated by treatment with shrimp alkaline phosphatase. Following phosphatase removal, the dephosphorylated CoA metabolites are quantitatively rephosphorylated by treatment with [gamma-33P]ATP plus a dephospho-CoA kinase. The resulting radioactive CoA metabolites are then separated by reverse-phase high-performance liquid chromatography and quantitated by scintillation counting. Due to the enzymatic radiophosphorylation, the assay is specific for CoA and its short chain thioesters and is sensitive to sub-picomole levels of these compounds.     

A radiochemical procedure for the assay of fatty acid binding by proteins

Protein-bound and unbound fatty acids can be efficiently separated at 0 degree C using a hydrophobic column-packing material (Lipidex 1000) similar to the separation of protein-bound and unbound steroids (E. Dahlberg, M. Snochowski, and J.-A. Gustafsson (1980) Anal Biochem. 106, 380-388). Protein-bound fatty acids are also removed by Lipidex 1000 when treatment is performed at 37 degrees C. Lipidex 1000 does not exhibit binding properties for soluble proteins at 0 and 37 degrees C, in contrast to dextran-coated charcoal. Lipidex 1000 appeared to be useful for the delipidation of protein samples at 37 degrees C and for a radiochemical assay of fatty acid-binding by microgram amounts of protein at 0 degree C. With this assay we obtained results on palmitate binding to serum albumin similar to those reported on the basis of equilibrium dialysis. Delipidated proteins from dealbuminized rat liver cytosol maximally bind about 4 nmol palmitate/mg protein.     

A rapid and sensitive radiochemical assay for phosphatidic acid phosphohydrolase activity.

A technique is described for the radiochemical assay of phosphatidic acid phosphohydrolase activity in rat brain. Radiochemically pure 32P-labeled phosphatidic acid of known specific radioactivity and structure, which was biosynthesized in vitro by the diacylglycerol kinase of E. coli, was used as the substrate. As little as 5 microgram of microsomal or mitochondrial protein can be used for the assay, and product formation in the picomole range can be determined accurately. This procedure should be useful in situations where only limited amounts of tissue are available.     

Purine enzyme activities in peripheral blood mononuclear cells: comparison of a new non-radiochemical high-performance liquid chromatography procedure and a radiochemical thin-layer chromatography procedure

Purine enzyme activities are usually assayed by radiochemical procedures and often TLC is part of the separation method. In screening patients with rheumatic diseases, these procedures have shown disadvantages like a relatively large coefficient of variation (C.V.) and time-instability. We describe a non-radiochemical reversed-phase HPLC micro-method with UV detection for measurement of activities of purine 5′-nucleotidase (5′NT; EC 3.1.3.5), purine nucleoside phosphorylase (PNP; EC 2.4.2.1) and hypoxanthine guanine phosphorybosyltransferase (HGPRT; EC 2.4.2.8) in human peripheral blood mononuclear cells (PBMC). The HPLC procedure is compared with the radiochemical TLC procedure by testing both with a 5′NT and a PNP assay. Reproducibility is tested with 14 healthy controls in each procedure. Short-term and long-term time-stability is tested by comparing enzyme activities measured immediately after preparation of the PBMC (week 0) with those found after freezing and storage at −20°C for a maximum of 10 weeks. The HPLC procedure is preferable to the radiochemical TLC procedure because it shows significantly better reproducibility and better time-stability and in addition is non-radiochemical and less time-consuming.     

A rapid procedure for assaying nicotinamide phosphoribosyltransferase

We examined the potential use of bovine enterokinase for the limited proteolysis of proteins containing sequences of one or more acidic residues preceding a basic residue. Proteolysis was followed by observing the appearance of fragments by sodium dodecyl sulfate-gel electrophoresis. The susceptible peptide bond was identified from a knowledge of the size of the fragment and the amino acid sequence of the protein. Bovine serum albumin was resistant to proteolysis in its native state, was somewhat susceptible as the S-carboxyamidomethyl derivative, and was highly susceptible as the S-carboxymethyl derivative. S-Alkylated soybean trypsin inhibitor and hen egg white lysozyme were both susceptible to limited hydrolysis, but only in the presence of deoxycholate. All susceptible bonds were either lysine or arginine. The preceding acidic residues could be either aspartic acid, glutamic acid, or carboxymethyl cysteine. If a single acidic residue immediately preceded the basic residue, the rate of hydrolysis was slow. The rate of hydrolysis was also slow if a carboxymethyl cysteine was introduced at the position following the basic residue. In addition to better defining the specificity of enterokinase, these results indicate that enterokinase may be useful in amino acid sequence studies for the production of large fragments. The enzyme may also be useful in DNA-recombinant studies in releasing the desired polypeptide chain from neighboring sequences.     

A rapid screening procedure for staphylococcal plasmids

A method has been developed for rapidly screening representatives of all currently recognized species of the genus Staphylococcus for the presence of plasmid DNA. The isolated plasmid DNA is substantially free from contaminating chromosomal and relaxed plasmid DNA. The method will detect plasmids in strains grown on various types of solid or liquid culture media and is convenient enough for routine epidemiological studies.     

A rapid procedure for isolating hemopoietic cell nuclei

A new method for isolating cell nuclei is described which involves freezing and thawing cells in 2% Tween 40, then gentle homogenization to release nuclei, followed by immediate microcentrifugation through 50% sucrose. Purified nuclei were obtained in 3 min and yields of 78-95% were obtained from a variety of human hemopoietic cells. Electron microscope analysis of nuclei obtained from HL60 cells showed that 89% of the nuclei were intact and have an appropriate morphology. A low level of contamination with other organelles was revealed by electron microscopy and by using specific assays for plasma membrane, mitochondria, lysosomes, Golgi membrane, and endoplasmic reticulum (0.5-5.5%). The value of the technique is that nuclear proteins and small metabolites which might be lost by rapid leakage from isolated nuclei and the possibility of biochemical modification of cellular constituents are minimized by using a rapid isolation procedure.     

A rapid radioassay procedure for plasma lecithin-cholesterol acyltransferase

A rapid and accurate single step procedure is described for the assay of lecithin-cholesterol acyltransferase activity. After incubation, using radiolabeled cholesterol as the substrate, an ethanolic solution of digitonin is added directly to the incubation mixture to extract the lipids. Excess cholesterol is then added, and the labeled cholesterol-digitonide along with denatured proteins are sedimented by low speed centrifugation, leaving the labeled esterified cholesterol in solution. An aliquot of the supernatant is counted in an aqueous scintillation mixture. The method correlates well with the established thin-layer chromatographic procedure using either lecithin-cholesterol vesicles or heat-inactivated plasma as the substrate for lecithin-cholesterol acyltransferase.     

The radioreceptor assay: a simple, sensitive and rapid analytical procedure

Radioreceptor assays (RRAs) are analogous in concept to radioimmuno assays. Characteristic to both methods is the saturable, specific, competitive and reversible ligand/receptor interaction. The RRA is simple, sensitive and reproducible and provides a degree of precision comparable to more sophisticated analytical techniques. Since RRAs require little specialized equipment, they can be used routinely by any laboratory engaged in biochemical research or, as an inexpensive exercise to teach the fundamentals of ligand binding and analytical pharmacology.     

Simple and rapid procedure for the purification of lipoprotein(a)

Lipoprotein(a) [Lp(a)] is a low-density lipoprotein-like particle displaying strong athero-thrombotic properties. Highly purified Lp(a) is increasingly requested for standardization of Lp(a) measurements and for biological studies. Several procedures have been described for Lp(a) separation and purification but none of them appear completely suitable. We present here a procedure for Lp(a) purification based on sequential elutions after lysine-Sepharose affinity chromatography. We were able to identify four distinct subspecies of Lp(a) showing different affinity to ε-amino groups of lysine-Sepharose, simply by modifying molarity and pH of the eluents; the fraction obtained in highly purified state represented the major form and could be eluted with 0.5 M sodium phosphate buffer (pH 4.4). Advantages of this procedure are represented by simplicity, rapidity and final yield.     

Anaerobic bacterial reductions of aldehydes and ketones: a rapid screening procedure

A semi-quantitative screening procedure is described whereby the abilities of cell-free extracts of bacteria to oxidize a selection of alcohols are rapidly disclosed. The activities displayed in the preliminary screen generally correlate well with the relative abilities of washed suspensions of these bacteria to reduce the corresponding aldehydes and ketones. The method therefore promises to be helpful in informing the choice of the most appropriate bacterium wherewith to effect the bioreduction of any particular ketone.     

Mouse nerve growth factor: a rapid isolation procedure for the alpha and gamma subunits.

A rapid method for isolating the α and γ subunits of mouse submaxillary gland nerve growth factor, as by-products of the commonly used Bocchini-Angeletti (2.5 S) procedure, has been devised. Approximately 40 mg of each subunit is obtained from 400 pairs of adult glands. The subunits isolated in this fashion are indistinguishable from those obtained from the homogeneous 7 S complex as judged by gel electrophoresis or their association-dissociation behavior.     

GATES: a rapid and powerful gene-based association test using extended Simes procedure

The gene has been proposed as an attractive unit of analysis for association studies, but a simple yet valid, powerful, and sufficiently fast method of evaluating the statistical significance of all genes in large, genome-wide datasets has been lacking. Here we propose the use of an extended Simes test that integrates functional information and association evidence to combine the p values of the single nucleotide polymorphisms within a gene to obtain an overall p value for the association of the entire gene. Our computer simulations demonstrate that this test is more powerful than the SNP-based test, offers effective control of the type 1 error rate regardless of gene size and linkage-disequilibrium pattern among markers, and does not need permutation or simulation to evaluate empirical significance. Its statistical power in simulated data is at least comparable, and often superior, to that of several alternative gene-based tests. When applied to real genome-wide association study (GWAS) datasets on Crohn disease, the test detected more significant genes than SNP-based tests and alternative gene-based tests. The proposed test, implemented in an open-source package, has the potential to identify additional novel disease-susceptibility genes for complex diseases from large GWAS datasets.     

Insulin-like growth factor I/somatomedin-C: a rapid isolation procedure with FPLC

Insulin-like growth factor I (IGF I)/somatomedin-C (SM-C) was purified from lyophilized human serum by acid-ethanol extraction. The extract was precipitated with acetone-ethanol. The precipitate was purified by Sephadex G-50 chromatography. The protein peak within a molecular weight range of 5000-10 000 was further purified with FPLC-reversed phase chromatography using a Pep RPC HR 5/5 column (Pharmacia) with a solvent system of acetonitrile (CH3CN) and 0.1% trifluoroacetic acid (TFA) in water. The purification of IGF I was monitored by radioimmunoassay for SM-C. Purity was established by analytical isoelectric focusing and by SDS polyacrylamide gel electrophoresis. Analytical isoelectric focusing showed one single protein band with an apparent pI of 8.3 +/- 0.1. SDS polyacrylamide gel electrophoresis showed also one single protein band with an apparent molecular weight of 7000. Biological activity was demonstrated by measuring the (3H)thymidine incorporation into DNA of cultured arterial smooth muscle cells.