Effect of temperature and protein concentration on the protein types within the ultracentrifugation supernatant of liquid micellar casein concentrate

Liquid micellar casein concentrate (MCC) is an ideal milk-based protein ingredient for neutral-pH ready-to-drink beverages. The texture and mouthfeel of liquid MCC-based beverages depend on the beverage protein content, as well as the composition of soluble proteins in the aqueous phase around the casein micelle. The objective of this study was to determine the composition of soluble proteins in the aqueous phase around the casein micelles in skim milk and liquid MCC containing 7.0% and 11.6% protein content. Skim milk was pasteurized and concentrated to 7% protein content by microfiltration and then to 18% protein content by ultrafiltration. The 18% MCC was then serially diluted with distilled water to produce 11.6% and 7.0% protein MCC. Skim milk, 7.0% MCC, and 11.6% MCC representing starting materials with different protein concentrations were each ultracentrifuged at 100,605 × g for 2 h. The ultracentrifugation for each of the starting materials was performed at 3 different temperatures: 4°C, 20°C, and 37°C. The ultracentrifugation supernatants were collected to represent the aqueous phase around the casein micelle in MCC solutions. The supernatants were analyzed by Kjeldahl to determine the crude protein, casein, and casein as a percentage of crude protein content, and by sodium dodecyl sulfate PAGE to determine the composition of the individual proteins. Most of the proteins in MCC supernatant (about 45%) were casein proteolysis products. The remaining proteins in the MCC supernatant consisted of a combination of intact αS-, β-, and κ-caseins (about 40%) and serum proteins (14-18%). Concentrations of αS-casein and β-casein in the supernatant increased with decreasing temperature, especially at higher protein concentrations. Temperature and interaction between temperature and protein explained about 80% of the variation in concentration of supernatant αS- and β-caseins. Concentration of supernatant κ-casein, casein proteolysis products, and serum protein increased with increasing MCC protein concentration, and MCC protein concentration explained most of the variation in supernatant κ-casein, casein proteolysis products, and serum protein concentrations. Predicted MCC apparent viscosity was positively associated with the dissociation of αS- and β-caseins. Optimal beverage viscosity could be achieved by controlling the dissociation of these proteins in MCC.

Identification of reference genes for microRNAs of extracellular vesicles isolated from plasma samples of healthy dogs by ultracentrifugation, precipitation, and membrane affinity chromatography methods

OBJECTIVE

To compare ultracentrifugation, precipitation, and membrane affinity chromatography methods for isolation of extracellular vesicles (EVs) from canine plasma samples and to identify suitable reference genes for incorporation into a quantitative reverse transcription PCR assay of microRNA expression in plasma EVs of healthy dogs.

ANIMALS

6 healthy Beagles.

PROCEDURES

Plasma samples were obtained from each dog, and EVs were isolated from 0.3 mL of these samples via ultracentrifugation, precipitation, and membrane-affinity chromatographic methods. Nanoparticle tracking analysis was performed to determine the concentration and size distribution of EVs isolated by the ultracentrifugation method. Expression levels (cycle threshold values) of 4 microRNAs (let-7a, miR-16, miR-26a, and miR-103) were then compared by means of quantitative reverse transcription PCR assay. Three statistical programs were used to identify the microRNAs most suitable for use as reference genes.

RESULTS

Results indicated that ultracentrifugation was the most stable of all 3 methods for isolating microRNAs from 0.3 mL of plasma. Nanoparticle tracking revealed that EV samples obtained by the ultracentrifugation method contained a mean ± SD of approximately 1.59 × 10¹⁰ vesicles/mL ± 4.2 × 10⁸ vesicles/mL. Of the 4 microRNAs in plasma EVs isolated by ultracentrifugation, miR-103 was the most stable.

CONCLUSIONS AND CLINICAL RELEVANCE

The ultracentrifugation method has potential as a stable method for isolating EVs from canine plasma samples with a high recovery rate, and miR-103 may provide the most stable reference gene for normalizing microRNA expression data pertaining to plasma EVs isolated by ultracentrifugation.

Detection of nodavirus in seawater from rearing facilities for Atlantic halibut Hippoglossus hippoglossus larvae

We used (1) ultracentrifugation followed by RT-PCR and (2) real-time RT-PCR to detect and quantify nodaviruses in seawater in which Atlantic halibut Hippoglossus hippoglossus larvae/fry had been held at rearing facilities. Evaluated against in vitro propagated viruses, the viral concentration corresponded to 1.6 x 10(4) TCID50 (50% tissue culture infectious dose) ml(-1). Evaluated against in vitro transcribed RNA, the concentration was estimated at 2 x 10(7) virus particles ml(-1) seawater.

Determination of Bovine Serum Low-density Lipoprotein Cholesterol using the N-geneous Method

The N-geneous method is a recently developed method for determination of low-density lipoprotein cholesterol (LDL-C) in human serum. In the present study, we attempted to adapt this method to bovine serum. The values of LDL-C obtained using the N-geneous method were highly correlated with those from the method using ultracentrifugation and heparin sepharose affinity chromatography (r = 0.934, p < 0.001). The reproducibility of this method was acceptable (intra-assay CV 4.2%, inter-assay CV 7.6%) for clinical use. Using the N-geneous method, serum LDL-C was evaluated in cows around parturition, and in cows with fatty liver induced by fasting. The concentration of LDL-C decreased significantly in cows close to parturition. A reduced concentration of LDL-C was also observed in cows with fatty liver. In both cases, the changes of LDL-C were similar to those of apolipoprotein B (apoB)-100, and the values of LDL-C were highly correlated (r = 0.876, p < 0.001) with those of apoB-100. These results suggest that the concentration of LDL-C reflects the level of apoB-100. The N-geneous method is simple and rapid, and might to be a useful tool to elucidate the clinical significance of LDL-C in bovine serum.

Bovine Paraoxonase 1 Activities in Serum and Distribution in Lipoproteins

Paraoxonase 1 (PON1) is an enzyme associated with high-density lipoprotein (HDL) and has a protective effect against oxidation of lipoproteins in mammals. We investigated PON1 enzyme activities in bovine serum and its distribution among bovine serum lipoproteins. Paraoxonase activity and arylesterase activity in serum (152 Holstein cows and 42 Japanese Blacks) were 275 +/- 55 U/ml and 130 +/- 27 U/ml (mean +/- SD), respectively. There was a high correlation (r=0.962) between the two enzyme activities, and the activity ratio of paraoxonase/arylesterase did not exhibit individual variation. More than 85% of both paraoxonase and arylesterase activities were detected in the HDL fraction separated by ultracentrifugation. The 43-kDa protein in the HDL fraction was identified as bovine PON1 by N-terminal amino acid sequence analysis. Bovine PON1 was purified by ultracentrifugation and preparative sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and an anti-bovine PON1 antiserum was developed. The concentration of PON1 protein determined by immunoblotting was closely correlated (r=0.976) with paraoxonase activity in serum. Bovine HDL was further fractionated into subpopulations, and the distribution of PON1 was examined. Paraoxonase activity and PON1 protein increased with decreasing HDL size and approximately 60% of total paraoxonase activity was distributed in the heavy HDL fraction. The different distributions of PON1 among HDL subpopulations might be concerned to the function and metabolism of bovine HDL.

Vitamin A excreted in the urine of canines is associated with a Tamm-Horsfall like protein

Under physiological conditions canines transport vitamin A in blood plasma primarily as retinyl esters bound to lipoproteins and excrete substantial amounts of vitamin A as retinol and retinyl esters with urine. In the aqueous environment of urine, the hydrophobic vitamin A has to be associated with a protein. This vitamin A-protein complex was purified to homogeneity, prepared by preparative ultracentrifugation (density 1.21 g/mL), native polyacrylamide gel electrophoresis (PAGE) and size exclusion chromatography. The vitamin A-protein complex has a high molecular mass of > 5,000 kDa under native conditions. SDS PAGE under reduced conditions revealed a single band with a molecular mass of about 100 kDa for the protein moiety. Peptides obtained after limited proteolysis with trypsin from the 100 kDa protein were characterised by MALDI-TOF mass spectrometry and showed amino acid sequence homology to the human Tamm-Horsfall Protein (THP). This was further confirmed by a positive immunoreaction of the isolated protein with crossreacting human THP antibodies. The localisation of THP in dog kidneys was determined by using immunohistology. The reaction was strong along the entire thick ascending limb ofthe Henle loop and distal convoluted tubule. Our data point to the possibility that THP functions as a novel carrier for vitamin A in the urine of canines.

Ultrastructure of centrifuged bovine oocyte-cumulus complexes after pre-treatment with cytoskeletal relaxant

The objective of this study was the electron microscope examination of the localization of lipid droplets, mitochondria and other intracellular organelles in bovine oocytes and cumulus cells after Cytochalasin B pre-treatment and ultra-centrifugation. Bovine (n = 180) oocyte cumulus complexes on a germinal vesicle stage were treated with 5 micrograms/ml Cytochalasin B at 38.5 degrees C for 10-15 min. They were then centrifuged at 15,800 g and fixed at 39 degrees C immediately after centrifugation in 3% glutaraldehyde with 0.5% formaldehyde for the microscopic examinations. The centrifugal pole of the oocytes was filled with mitochondria. The centripetal part contained lipid granules and vesicles. Cytoplasm of low density was located in the equatorial region. Hyaloplasm with spontaneously formed membrane and non-membrane vacuoles was located in a supra-equatorial zone of the oocytes. In the cumulus cells the lipid vesicles formed one dark mass in the centripetal pole. The nuclei of these cells were deformed and vacuolization of the cytoplasm was noted.

Hypercholesterolemia in Shetland sheepdogs

Plasma lipoprotein cholesterol in 64 clinically healthy Shetland sheepdogs was evaluated to assess whether the breed is more susceptible to hypercholesterolemia. The incidence of hypercholesterolemia was clearly higher in Shetland sheepdogs and mean plasma cholesterol level was significantly higher in Shetland sheepdogs than in control dogs. Blood biochemical examinations did not evidence the abnormalities, which imply the causative disorders, and thyroid hormone levels were not significantly different from the controls. These results suggest that the cholesterolemia is a primary disorder. Cholesterol fractionation by agarose gel electrophoresis and ultracentrifugation revealed that accumulation of alpha2-migrating lipoproteins was the common characteristic of dogs showing cholesterol level over 250 mg/dl in the breed. Increase in prebeta-beta-lipoproteins was also found in Shetland sheepdogs with marked hypercholesterolemia over 500 mg/dl. Therefore. Shetland sheepdogs may include more dogs with primary disorders in lipoprotein metabolism, which cause hypercholesterolemia. at least in Japan.

Purification and characterization of liver ferritins from different animal species

The ferritins were purified from liver homogenates of buffalo, camel, cattle, sheep and shark by thermal denaturation, ammonium sulphate fractionation, Sephacryl S-300 gel filtration and DEAE-blue gel affinity chromatography. The yield and iron content of affinity-purified liver ferritins ranged from 0.008 to 0.052 mg/g and 3.17% to 11.4% respectively. As they are glycoproteins, the ferritins contained variable amounts of neutral carbohydrates. Except for shark ferritin, the ferritins all exhibited immunological cross-reactivity with anti-buffalo liver ferritin and anti-horse spleen ferritin by immunodiffusion and immunoelectrophoresis. Gel electrophoresis, gel filtration and ultracentrifugal analysis indicated the presence of a monomeric ferritin in all cases. SDS-gel electrophoresis of shark ferritin gave a protein band of 18 kDa. Ovine, buffalo and bovine ferritin comprised two protein subunits, the H (20 and 21 kDa) and the L types (18 and 19 kDa). Oligomeric ferritin subunits with molecular weights of 27, 37 and 55 kDa were also found for bovine and buffalo ferritin. SDS-PAGE of camel ferritin revealed a complex pattern with four prominent bands of 61, 51, 44 and 39 kDa. Two fast-migrating components of 15 and 16 kDa were also found in the purified liver ferritins, including reference preparations. The PO4(3-)/Fe ratios of purified shark (0.10) and bovine ferritin (0.12) were similar to that of standard equine spleen ferritin (0.11). However, the ratio was higher in ovine (0.17), camel (0.22) and bovine (0.26) ferritins. The amino acid compositions, molecular weights and sedimentation coefficients of the different liver ferritins were similar.

Stunting syndrome in turkey poults: isolation and identification of the etiologic agent

Stunting syndrome (SS) is an enteric disease of turkey poults that causes high morbidity including reduced growth, impaired feed efficiency, and diarrhea. The etiologic agent of this disease has not been previously reported. The objectives of the present study were to identify, isolate, and purify the etiologic agent of SS. Day-old poults were orally inoculated with a SS-inducing inoculum. The intestinal epithelial cells (IECs) were isolated on the fourth day postinoculation. The IECs were lysed and filtered through 0.2-, 0.1-, and 0.02-micron filters. The cell lysate filtrate (0.1 micron) was subjected to density gradient ultracentrifugation. Intact IECs, filtrates from IECs (0.2, 0.1, and 0.02 micron ), and IEC lysate fractions from gradients (FRG) were used as inocula to infect day-old turkey poults. The weight gain, jejunal maltase activity, and gross intestinal lesions were used as the parameters of evaluation. Weight gain and maltase activity were reduced (P = 0.001) by the isolated IECs, 0.2 and 0.1 micron filtrates, and FRG when compared with corresponding controls. IEC lysate filtrate (0.1 micron) and FRG were examined under transmission electron microscope (EM). Enveloped, pleomorphic particles varying in size from 60 to 95 nm were observed and termed stunting syndrome agent (SSA). Primary cultures of turkey IECs were used to further isolate and propagate the SSA. Following the fifth passage in the turkey IECs, the cell lysate induced SS in day-old poults. SSA particles were observed under EM after the fifth passage. The results of this study provide evidence that a viral agent has been isolated and identified from IECs of SS-infected poults and is the etiologic agent of SS.

Ultracentrifugal and electrophoretic characteristics of the plasma lipoproteins of miniature schnauzer dogs with idiopathic hyperlipoproteinemia

To better characterize the idiopathic hyperlipoproteinemia of Miniature Schnauzer dogs, the plasma lipoproteins of 20 Miniature Schnauzers (MS) and 11 dogs of other breeds (DOB) were evaluated by ultracentrifugation, electrophoresis, and biochemical tests. Seventeen MS were healthy; 3 had diabetes mellitus. Plasma from 6 of 17 healthy and all 3 diabetic MS was visibly lipemic. Lipemia was slight to marked in healthy lipemic MS, and marked in diabetic ones. All DOB had clear plasma; 8 were healthy and 3 had diabetes. All healthy lipemic MS and diabetic lipemic MS had hypertriglyceridemia associated with excess very low density lipoproteins. Chylomicronemia was present in 4 of 6 healthy lipemic MS and all 3 diabetic lipemic MS. Lipoproteins with ultracentrifugal and electrophoretic characteristics of normal low density lipoprotein were lacking in 4 of 6 healthy lipemic MS. The lipoprotein patterns of 4 of 11 healthy nonlipemic MS were characterized by mild hypertriglyceridemia associated with increased very low density lipoproteins and a lack of lipoproteins with characteristics of normal low density lipoproteins. Lipoprotein patterns of diabetic DOB closely resembled those of healthy DOB; those of diabetic lipemic MS resembled those of markedly lipemic healthy lipemic MS. In conclusion, the hyperlipoproteinemia of Miniature Schnauzers is characterized by increased very low density lipoproteins with or without accompanying chylomicronemia; some affected dogs may have decreased low density lipoproteins.

Isolation and characterization of the immunoglobin of pike (Esox lucius L.)

The purification of the immunoglobul in from pike serum and its physicochemical characterization is presented. The immunoglobul in was prepared by means of gel filtration and ion exchange chromatography. Measurements in the analytical ultracentrifuge showed a sedimentation constant of 15.0 S. A molecular weight of 650.000 was calculated. The immunoglobulin was composed of heavy and light chains of molecular weights 60.000 and 22.500, respectively. It is likely that the immunoglobulin of pike is composed of 8 heavy and 8 light chains and possesses a tetrameric structure. The heavy chains contain 9.2% sugars and amino sugars. The amino acid composition of the chains is similar to that of other fish immunoglobulins.