C. Scolozzi

In vitro assessment of salvage pathways for pyrimidine bases in rat liver and brain

In this paper we extend our previous observation on the mobilization of the ribose moiety from guanosine to xanthine catalyzed by rat liver extracts (Giorgelli et al., Biochim. Biophys. Acta 1335 (1997) 16-22). The data show that in rat liver and brain extracts the activated ribose, stemming from inosine and guanosine phosphorolysis as ribose 1-phosphate, can be used to salvage uracil to uracil nucleotides. Uridine is an intermediate. The salvage process occurs even in the presence of excess inorganic phosphate suggesting that uridine phosphorylase may function in vivo as an anabolic enzyme. Ribose 5-phosphate cannot substitute for inosine, guanosine or ribose 1-phosphate as ribose donor. When inorganic phosphate was substituted with arsenate, hindering the formation of ribose 1-phosphate, no ribose transfer could be observed. A similar pathway occurs at the deoxy level. The deoxyribose moiety of deoxyinosine can be used to salvage thymine to thymine nucleotides, again in the presence of excess inorganic phosphate. Our results introduce a novel aspect of the salvage pathway, in which ribose 1-phosphate seems to play a pivotal role.

Recycling of α-d-ribose 1-phosphate for nucleoside interconversion

Mobilization of the ribose moiety and of the amino group of guanosine may be realized in rat liver extract by the concerted action of purine nucleoside phosphorylase and guanase. Ribose 1-phosphate formed from guanosine through the action of purine nucleoside phosphorylase acts as ribose donor in the synthesis of xanthosine catalyzed by the same enzyme. The presence of guanase, which irreversibly converts guanine to xanthine, affects the overall process of guanosine transformation. As a result of this purine pathway, guanosine is converted into xanthosine, thus overcoming the lack of guanosine deaminase in mammals. Furthermore, in rat liver extract the activated ribose moiety stemming from the catabolism of purine nucleosides can be transferred to uracil and, in the presence of ATP, used for the synthesis of pyrimidine nucleotides; therefore, purine nucleosides can act as ribose donors for the salvage of pyrimidine bases.

Cheese making aptitude and the chemical and nutritional characteristics of milk from Massese ewes

Abstract The purpose of this study was to determine the effects of season, locality and the different altitudes at which farms are located, on the physico-chemical composition, morphometric characteristics of fat globules, fatty acid composition and cheese making aptitude of milk of Massese ewe’s raised in 11 flocks from two provinces of north-west Tuscany (Massa Carrara and Lucca). The winter lactation shows higher percentages of casein, lactose and not fat dry matter (P≤0.01); curd firming time (k20) is significantly lower and there is a greater curd firmness (a30) (P≤0.01); while in the summer there is a higher percentage of lipids (P≤0.01). The effect of the season significantly influences (P≤0.01) the size of the fat globules and impacted significantly on the fatty acids composition of the milk. In the hills the milk has a higher percentage of dry matter, protein, casein, fat, phosphorous and not fat dry matter (P≤0.01), whereas it has a lower percentage of lactose and calcium (P≤0.05). The Somatic Cell Count (SCC) and the Total Bacterial Count (TBC) are statistically greater on the plains (P≤0.01), while milk produced in the hills shows higher quantity of α-linolenic acid and lower saturated fatty acids (P≤0.05). In the two typical rearing areas for Massese ewes we found differences amongst dry matter, fat, phosphorous and SCC, higher (P≤0.01) in the province of Massa Carrara that also had the best rheological parameters, but we found the highest cheese yield (P≤0.05) in the province of Lucca where there are also the greatest weight loss (P≤0.01). The milks produced in the winter season and in hilly areas present the best physico-chemical and nutritional characteristics. However, we found that the technological side should be improved by diversifying cheese-making techniques in relation to the characteristics of milk. In fact, currently these techniques do not fully exploit the potential to transform those milks with the best qualitative characteristics.

Morphometric analysis of fat globules in ewe's milk and correlation with qualitative parameters

Abstract In this study the morphometric characteristics of fat globules from ewe’s milk have been correlated with the chemical and technological parameters of the milk. Milk samples were taken from twenty-five Massese ewes, subdivided according to the parity; the animals were homogeneous for lactation phase and diet. The morphometric analysis of fat globules (n./ml, diameter, surface area/volume), the standard chemical analysis, SCC and determination of the rheological parameters were performed on milk samples obtained during the morning milking. The mean number of fat globules/ml was 3.09 x 109, with a mean diameter of 3.93 µm, ranging from 1.20 µm to 12.30 µm. For all parities, a fat globule diameter ranging from 3.21 to 4.20 µm was found most frequently. Animals in the first lambing order showed a significantly lower percentage (5.26%) of large globules (>5.21µm), while animals in the fifth lambing order showed a higher percentage (20.75%). The number of globules/ml was negatively correlated to milk production (P≤0.01) and curd firmness at 45 min (P≤0.05); whereas it was positively correlated to protein content, non-fat dry matter, and curd firming time (P≤0.05). Fat globule dimensions varied according to the parity of the animals and influenced various qualitative parameters of the milk.

The influence of b-lactoglobulin genetic polymorphism on morphometric characteristics of milk fat globules and milk fatty acids composition in Italian Friesian cow

Abstract β-lactoglobulin (β-Lg) is the major whey protein in the milk of ruminants and some non-ruminants. It was first isolated 60 years ago and a wealth of physico-chemical and biological information has been accumulated. Results of studies on the effect of β-Lg genotypes on milk production traits (milk yield, protein and fat yield) and on milk coagulation parameters have been rather consistent. In this study we evaluated the relationship between genetic polymorphism of β-Lg morphometric characteristics of fat globules and fatty acids composition of cow milk. The trial was carried out on 89 unrelated pluriparous Friesian dairy cows reared in the same herd in a medium-temperate climatic zone in the province of Pisa. All animals were fed the same diet. Individual milk samples were collected and analyzed in a triplicate. One milk sample of milk was collected for each cow and no preservative was used. Genotypes were determined by isoelectric focusing analysis of single milk sample. Milk fatty acids composition and morphometric characteristics of fat globules were analysed on each milk sample in triplicate. The frequency distribution of total measured milk fat globules was evaluated according to their size. Fat globule diameters were divided into nine classes of 1.5 µm width: from class 1 (1.5-3 µm) to class 9 (>13.5 µm). Finally, fat globules were further classified into two groups: group S (1.5-6 µm), and group L (>6 µm). The analysis of variance was carried out to evaluate the effect of β-Lg genotype on all evaluated parameters with simultaneous adjustment for sampling season, parity, and days from calving as a covariate. As reported in literature, a higher gene frequency of the B variant of β-Lg was observed (0.59 vs 0.41). Significant effects of β-Lg genotype were observed for the percentage of the number of fat globules in the 8th (12-13.5 µm) and 9th class (>13.5 µm) which were higher in the AB genotype than in the other genotypes. The C20:4ω6 content was significantly higher in the AB genotype (P<0.05) and C15:1 content was significantly higher in the AA genotype (P<0.05) than in the other genotypes. Although β-Lg genotypes would seem to have limited relationships with the dimensions of fat globules of cows’ milk, the higher content of C20:4ω6 in AB genotype is of particular interest from the nutritional point of view.

Regulation of Calf Thymus Cytosolic 5’-Nucleotidase/Nucleoside Phosphotransferase

Many phosphatases with different specificity and cellular location have been described to be able to catalyze a phosphotransferase reaction1, 2 as well as several enzymes named phosphotransferases have been demonstrated to hydrolyze phosphoesters3, 4. Even though a number of papers and very accurate reviews have been published on phosphohydrolases, particularly on nucleotidases classified following their substrate specificity or cellular location, still additional information is needed on the molecular characteristics and on the regulation of the phosphohydrolase/phosphotransferases in order to understand the role, if any, of their potential bifunctionality.

Study on chemical and fatty acid modifications of cow’s milk in relation to fat globules diameter

Riassunto Studio delle modificazioni delle caratteristiche chimiche ed acidiche del latte bovino in relazione alle dimensioni dei globuli di grasso. In questo studio è stato rilevato come la maggiore presenza nel latte di globuli di grasso con diametro inferiore a 6 µm risulti correlata positivamente alla percentuale di sostanza secca e lipidi, mentre la presenza di globuli con diametro superiore a tale valore favorirebbe una maggiore produzione di latte, una percentuale più elevata di lattosio, sostanza secca magra e ceneri. In relazione al contenuto in acidi grassi, latti con percentuali più elevate di globuli al di sotto del valore di 6 µm tenderebbero ad essere più ricchi in acidi grassi insaturi C18:1, C18:2 e CLA, mentre globuli di grasso di dimensioni superiori favorirebbero una prevalenza di acidi grassi saturi (C6:0, C8:0, C10:0, C12:0, C14:0, C16:0, C20:0, C21:0, C22:0), oltre che di C20:2 e C18:3 ω3. Sulla base di questi risultati il diametro dei globuli di grasso pari a 6 µm potrebbe essere considerato come “valore soglia” per la definizione di alcune caratteristiche qualitative del latte bovino.