Use of polynucleotide/polyacrylamide-gel electrophoresis as a sensitive technique for the detection and comparison of ribonuclease activities

Isoelectric focusing--polynucleotide/polyacrylamide-gel electrophoresis. A technique to separate and characterize nuclease activities

Individual native nuclease activities from human leucocytes are separated by using two-dimensional gel electrophoresis in an apparatus that allows the simultaneous running of 28 gels. Proteins are separated by isoelectric focusing in a disc gel, followed by electrophoresis into a slab gel containing DNA. Protein denaturants are avoided in the second dimension by the use of a running pH well above the optimal pH for DNAase (deoxyribonuclease) activity. Electrophoresed gels are incubated in appropriate buffers to activate nuclease activity. After staining for intact DNA, the positions of active enzymes, unobscured by the presence of other proteins, are revealed as colourless spots in a reddish-purple field. The technique is easy to use and is sensitive to 50pg of DNAase I. Versatility is provided by the use of either acidic or basic electrophoresis running buffers and by the use of specific gel incubation conditions to reveal different sets of enzyme activities. Two DNAases active at pH 7.4 in the presence of Mg2+ and Ca2+, and sixteen DNAases active at acidic pH and not requiring metals, are detected. Treatment of the human enzymes with specific glycosidases reveals that many of the human DNAases are glycoproteins containing negatively charged moieties and may be derived from modification of parent activities.

A ribonuclease assay: Separation of product from undegraded aminoacyl-transfer RNA substrate

A new rapid microassay for RNase is based on the extraction of the products of the degradation of aminoacyl-tRNA into ethyl acetate. The substrate, for example, f[3H]Met-tRNA, is not soluble in ethyl acetate but the product f[3H]Met-nucleotide is extracted with high efficiency over a wide range of pH in phosphate buffer of high ionic strength. The limit digest of f[3H]Met-tRNA by RNase T1 in which the minimum-sized product should be f[3H]Met-hexanucleotide is also soluble in ethyl acetate. The assay is sensitive to 0.05 pg of RNase A, has a very low background, and is linear with enzyme concentration. The most economic substrate is unfractionated tRNA containing a small concentration of the radiolabeled aminoacyl-tRNA.

The ribonucleases of bovine skeletal muscle

Bovine skeletal muscle contains small amounts of at least six heat- and acid-stable RNA-degrading enzymes. Our results are the first evidence for multiple ribonucleases in skeletal muscle. Three of these have been highly purified, and each has been shown to be a pyrimidine-specific endoribonuclease by use of a rapid sequencing technique employing gel electrophoresis. However, synthetic co-polymers containing adenylate or guanylate residues in addition to pyrimidine residues are hydrolysed at higher rates than are the pyrimidine homopolymers. With 0.63 mM yeast RNA as substrate, all three enzymes (ribonucleases I, II and III) are optimally active in alkaline solution (pH 7.5-8.5) containing 0.05-0.15 M univalent salts, do not require bivalent cations, and have molecular weights of 13 000-20 000. The properties of muscle ribonuclease I are very similar to those of bovine pancreatic ribonuclease A. Muscle ribonucleases II and III have characteristics similar to those of ribonucleases found in various other bovine tissues. In common with all previously studied pyrimidine-specific endoribonucleases, the bovine muscle ribonucleases are inhibited by such purine homopolynucleotides as polyadenylate. Furthermore, polyamines, present in low concentrations, can reverse or regulate the amount of inhibition of enzyme activity.