Ribonuclease from human granulocytes

Acid ribonuclease and alkaline ribonuclease isoenzymes in plasma of patients with decreased glomerular filtration rate

Removal of low molecular weight proteins from plasma by kidneys depends on glomerular filtration rate (GFR), protein-glomerular membrane electric charge, steric interactions and a number of functionally active nephrons present in the kidneys. There is a well documented relationship between the concentration of low molecular weight proteins in plasma and GFR value in patients with impaired renal function. Accumulation of low molecular weight proteins in plasma along with a decrease in GFR value may in the long run enhance formation of protein tissue deposits known as various forms of amyloidosis. In this paper we present studies on plasma concentrations of acid leukocyte-type ribonuclease (RNase) and alkaline pancreatic-type RNase and GFR value in 54 patients with renal failure. RNase isoenzymes' activities were assayed by measuring their enzyme activities manifested as ability to decompose yeast RNA and assay of digestion products' concentration by spectrophotometry. The studies show that decreasing filtration rate produces an increase in serum activities of both acid and alkaline RNases, which is proportional to the logarithm of GFR value. However, the increase rate vs. GFR value is by four times higher for acid RNase then for alkaline RNase. Acid RNase in human plasma is mostly of leukocytic origin and differs from pancreatic-type alkaline RNase, which is of pancreatic origin. The obtained results may suggest that leukocyte originating proteins essentially contribute to low molecular weight protein accumulation in plasma of patients with chronic renal insufficiency.

Major Interference from Leukocytes in Reverse Transcription-PCR Identified as Neurotoxin Ribonuclease from Eosinophils: Detection of Residual Chronic Myelogenous Leukemia from Cell Lysates by Use of an Eosinophil-depleted Cell Preparation

Background: The extraction of RNA from leukocytes for reverse transcription-PCR (RT-PCR) is time-consuming and contributes to variation in analysis of the Philadelphia (Ph1) chromosome of chronic myelogenous leukemia (CML) by RT-PCR. To detect residual CML after bone marrow transplantation, mRNA from at least 105 leukocytes should be analyzed, but the RNase activity of the cells precludes simple leukocytes lysis as an alternative to RNA extraction. We sought to identify the main source of RNase activity of leukocytes.

Methods: We used a three-step chromatographic process and amino acid sequence analysis. We selected eosinophil-free granulocytes by using a biotinylated CD16 antibody and selected mononuclear cells by fractionating the leukocytes with a Ficoll-Paque® density gradient.

Results: Chromatography and amino acid sequencing identified eosinophil-derived neurotoxin (EDN) as the main source of leukocyte RNase. Depletion of eosinophils reduced the EDN content of cell lysates by ∼90%, allowing a signal from a lysate of 50 K562 Ph1-positive cells mixed with 105 CD16+ granulocytes that was equivalent to 77% of the signal in the absence of leukocytes. A similar lysate with mononuclear cells gave a signal equivalent to 53% of that without mononuclear cells. RNA extraction gave a signal equivalent to only 24% of the leukocyte-free control.

Conclusion: The depletion of eosinophils during the preparation of leukocyte samples for RT-PCR efficiently reduces the risk of mRNA degradation by ribonucleases, enabling RT-PCR analysis directly from cell lysates with a better signal than can be obtained by RNA extraction.

Ribonuclease inhibitors in human blood: comparative studies on the inhibitors detected in erythrocytes, platelets, mononuclear leukocytes and granulocytes

The erythrocyte ribonuclease inhibitor (RI) and platelet RI were separately purified to homogeneity and showed similar properties to those of human brain and placental RIs. The same type of RI seemed to be present in mononuclear leukocytes and granulocytes. The RI contents of these cells were detectable by immunoblot analysis using anti-human placental RI antibody. Neither RI activity nor the molecule cross-reactive with the anti-human placental RI antibody was detectable in any plasma sample. It is intriguing to detect active RI in mature erythrocytes, where no nucleus exists and RNA metabolism is unlikely to occur.

Ribonuclease from cytosolic fraction of human erythrocytes

Ribonuclease (RNase) activity is detectable in only one third of specimens of human erythrocyte haemolysates. On the other hand, treatment of erythrocytic cytosoles with sulphosalicylic acid reveals an inhibitor-bound RNase activity which is present in all erythrocyte specimens studied. The level of the erythrocyte inhibitor-bound RNase activity is comparable to that in human lymphocytes. Isolated RNase from the cytosolic fraction of human erythrocytes is poly-C avid RNase with maximum activity at pH 6.5. The enzyme is resistant to treatment with strong acids and heating up to 95 degrees C. Molecular filtration of the erythrocyte RNase shows that it is composed of two fractions differing in molecular mass, 19 000 and 15 000. No difference in enzymic properties between these fractions was found. The general properties of erythrocyte cytosolic RNase are much like those of acid RNases of human granulocytes and lymphocytes. As the erythrocytes do not metabolize RNA no function for the inhibitor-bound RNase can be suggested. Assuming that the observed erythrocyte RNase is the residual enzyme, persisting in the cell since it was functioning in the nucleated erythrocyte precursors, one may surmise that levels of free and inhibitor-bound erythrocyte RNase activity may be related to the normality or abnormality of erythrocyte maturation.

Sialic acid residues contribute to the heterogeneity of human serum ribonuclease: demonstration by isoelectric focusing and neuraminidase treatment of serum

Ribonuclease (RNase) activity from human serum appears as multiple zones of activity following isoelectric focusing in thin layer polyacrylamide gel. At least one but not all of these zones is cross reactive with rabbit antibovine pancreatic RNase A antiserum. Treatment of serum or partially purified serum RNase with neuraminidase reduces the complexity of the serum RNase banding pattern to a major band which focuses at a pH of 9.5 or greater and a minor zone of activity which focuses at about pH 6.0-6.2. Trypsin does not affect the pattern. Thus, sialic acid residues account for a large portion of the heterogeneity of human serum RNase. Neuraminidase treatment is requisite for evaluating RNase from serum and certain other sources.

Clinical significance of acidic pI isoenzyme of ribonuclease in human serum

Employing isoelectric focusing with an Ampholine column, the presence of three major pI isoenzymes (basic, neutral and acidic) of human ribonuclease (RNase) is demonstrated. The acidic pI isoenzyme was observed in pancreatic and hepatic cancer cells and in fetal pancreas and liver tissues, and was frequently detected in the sera of patients with pancreatic and hepatic cancer. This isoenzyme was not, however, detected in the sera of non-cancerous patients. In pancreatic cancer tissues, other pI isoenzymes, except for the acidic one, were markedly suppressed and the isoelectrophoretic patterns of the cancerous tissues closely resembled those obtained from fetal pancreatic tissue. These results suggest that the acidic pI isoenzyme could represent one of the carcinofetal proteins and that the detection of this pI isoenzyme in the patient's serum may be useful for the diagnosis of pancreatic and hepatic cancer.

Activities of serum acid ribonuclease in patients with malignant neoplasms or with renal failure

The activities of serum acid ribonuclease (RNase) were determined in patients with malignant neoplasm or with renal failure. The levels were markedly increased in myelogenous leukemia and renal failure, and only slightly increased in solid cancers, lymphoid malignancies and multiple myeloma. These increases correlated significantly with serum LDH activity in myelogenous leukemia and with creatinine levels in other malignancies or renal failure. The acid RNase content of granulocytes was 22.7-fold higher than that of lymphocytes. The increase of serum acid RNase may suggest an increased granulocyte destruction in myelogenous leukemia and a reduced glomerular filtration in other malignant neoplasms and renal failure.

Serum ribonuclease in the diagnosis of pancreatic carcinoma and in monitoring chemotherapy

Although serum ribonuclease (RNAase) activity (measured by Reddi's method [1]) was significantly higher in 24 patients with pancreatic carcinoma (mean 12.5 units) than in 93 control subjects (mean 5.0 units), 14 patients with chronic pancreatitis (mean 5.2 units) and 83 patients with other primary malignancies (mean 6.8 units), there was much overlap between the four groups and considerable (16.5%) inter-assay variation. Modification of the assay to eliminate a substrate inhibition effect gave acceptable inter-assay variation but abolished any significant difference between the four groups. Changes in serum RNAase activity did not reflect clinical changes in patients with pancreatic carcinoma followed serially during a trial of chemotherapy. The results indicate that serum RNAase is not a useful marker of pancreatic carcinoma.

The isolation, purification, and properties of a ribonuclease (Mr 18 000) from human uremic serum, and its relation to the human urinary ribonuclease (Mr 33 000). II. Properties of the enzymes

A low molecular weight ribonuclease (Mr 18 000) isolated and purified from human uremic serum was found to have similar properties to the high molecular weight ribonuclease (Mr 33 000) isolated from human urine. A detailed comparative study of both enzymes was undertaken to investigate the relationship between them. It is suggested that poly(C)-avid human ribonucleases have similar amino acid compositions but variable carbohydrate contents and that variations in the sugar content are responsible for variations in the molecular weight.

Purification and properties of ribonucleases from human urine

The two major ribonuclease (EC 3.1.27.5) present in normal human urine have been highly purified and extensively characterized for their enzymatic, physical, chemical and structural properties. One of the enzymes, RNAase C, is a glycoprotein which exhibits a pH optimum of 8.5 with RNA as the substrate and preferentially degrades the synthetic homoribopolymer poly(C). This enzyme is resolved into multiple components by column electrofocusing. However, prior treatment with neuraminidase results in a single form of RNAase C with an isoelectric point of 10.4, indicating that the charge heterogeneity is the result of variability in sialic acid content. Amino acid composition and NH2- and COOH-terminal sequence analyses of RNAase C show that this enzyme is very similar to mammalian pancreatic RNAases; the data indicate a peptide chain of 126 amino acid residues and a 33% carbohydrate content. The second enzyme isolated from urine, termed RNAase U, is also a glycoprotein which has a pH optimum of 7.0 with RNA as substrate and is virtually inactive against poly(C). RNAase U lacks sialic acid and focuses as a single component with a highly basic isoelectric point of greater than pH 11.0. The NH2- and COOH-terminal sequences of RNAase U show little homology with the pancreatic RNAases. However, the amino acid composition of this enzyme indicates it is very similar to human spleen RNAase.

Myeloperoxidase inactivation in the course of catalysis of chlorination of taurine

Myeloperoxidase (donor: hydrogen-peroxide oxidoreductase, EC 1.11.1.7) was isolated from leukocytes of patients with chronic granulocyte leukemia. In the presence of H2O2 and Cl- at pH 4.0-6.6 the myeloperoxidase catalyses chlorination of taurine to monochloramine taurine and simultaneously undergoes inactivation. The myeloperoxidase inactivation rate depends on the concentration of H2O2 and Cl-: both the initial rate of chlorination and myeloperoxidase inactivation rate increase with increasing concentration of H2O2. However, an increase in concentration of Cl- results in a decrease in enzyme inactivation. At a given H2O2 concentration, myeloperoxidase inactivation is a first order reaction, which implied that the enzyme may react with a substrate a limited number of times.

Ribonuclease activity in plasma and leucocytes of malnourished children

RNAase activity was measured in plasma and leucocytes of manourished children. In subjects suffering from kwashiorkor, alk. RNAase levels in plasma and leucocytes were markedly raised and they returned to normal after therapy. However, the enzyme activity was not altered in undernourished children. These data indicate that circulating level of alkaline. RNAase is not a useful parameter for detecting milder grades of protein-calorie malnutrition (PCM).

Epidermal nucleases. II. The multiplicity of ribonucleases in guinea-pig epidermis

Ribonuclease activity has been extracted from adult guinea-pig epidermis by sequential homogenization in dilute sodium acetate and sulfuric acid. The extracts were subjected to ammonium sulfate fractionation and to affinity and ion exchange chromatography. Three ribonucleases (I, II, III) were separated from the sodium acetate extract and 6(A, B1, B2, B3, C, D) were isolated from the sulfuric acid extract. The degree of purification varies from 65-fold to 8,700-fold and the apparent molecular weights of the active forms of 8 of the 9 ribonucleases range from 10,000 to 36,500. No phosphodiesterase activity is present in any of the 9 fractions, but there is alkaline phosphatase activity in one (I) and deoxyribonuclease activity in a second (B3). Two of the ribonucleases have acid pH optima (a1, B3), while the others are most active between PHs 6.8 and 7.8. The activity of 4 of the fractions is sensitive to added EDTA (III, A, B2, B3,), but no stimulatory metal ions were found. Low concentrations of the polyamine spermidine enhanced the activity of 3-fractions (III, C, D). Yeast ribonucleic acid is degraded exonucleolytically by 2 fractions (I, A) and endonucleolytically by the remaining 7. In experiments with homopolyribonucleotide substrates, poly U was generally the preferred substrate. Substantial hydrolysis of poly A occurred with 2 fractions (A, B3) and slight hydrolysis of poly G with 2 other fractions (B2, C).

Purification and properties of alkaline ribonuclease from human serum

1. Five alkaline ribonucleases (EC 3.1.4.22) were purified about 140- to 1900-fold from human serum by phosphocellulose and DEAE-cellulose chromatographies and Sephadex G-75 filtration, with a total recovery of 22%. These were designated as RNAases 1-5. 2. Optimum activities were observed at pH 8.5-8.7 for RNAases 1-4, and at pH 7.5 for RNAase 5. The molecular weights of these enzymes were estimated by gel filtration as 45 000, 32 000, 20 000, 13 000 and 8500, respectively. 3. These RNAases were found to be heat-labile proteins but are markedly stabilized with bovine plasma albumin. The reaction was activated by Na+, K+, Mg2+ and Ca2+, and inhibited by Co2+, Fe2+, Cu2+ and Zn2+. EDTA had little effect on the velocity of the reaction. Spermine caused 2- to 7-fold activation. 4. Among the substrates examined, these RNAases preferentially hydrolyzed pyrimidine bodies and except for RNAase 5 had a higher affinity for poly(C) than poly(U) as substrate. Each enzyme was free from other nucleolytic enzymes and hydrolyzed only RNA.