A method is described for the isolation ofthe fastest preal bumin fractionPA, from mouse serum. This fraction appears to behave identically to the urinary prealbumin fraction in electroMolecular weight is determined by diffusion and sedimentation as well as by sedimentation-The apparent lower molecular weight of serum prealbumin is due to its contamination by phoretic migration, strain and sex dependency and in immunological reactions. diffusion equilibrium.polysaccharides extracted from starch gel in the course of its isolation.Small laboratory rodents such as rats and mice are known to present an unusually high proteinuria. The mouse excretes some serum proteins and a major urinary protein isolated by Bao Linh et al. [l], was found to be of renal origin. Later, Finlayson et al. [2] showed hepatic synthesis of this last protein, this finding being in agreement with the results of Rumke and Thung [3] who found an immuno precipitation reaction of mouse serum treated with an antiserum against mouse urinary proteins. At pH 5.5 Finlayson et al. [4]found a separation of the major urinary protein into three peaks and made a phenotypic classification of mice on the basis of relative amounts of these components.In a previous publication [5] we have shown that urinary proteins of mice a t pH 8.6 migrate in starch gel almost entirely in the prealbumin zone as a single band and in agar as two bands I and 11. Moreover, 3 -4 bands are observed by agar electrophoresis in certain strains of mice. The fastest of the serum prealbumins observed by starch gel electrophoresis a t pH 8.6 called PA, has the same mobility as the urinary proteins and a considerable increase of this fraction in serum is observed after nephrectomy. Nevertheless, no immunochemical reaction is observed in the prealbumin zone after immunoelectrophoresis against antiurine rabbit serum.In the present work it will be shown that a positive result can be obtained with preparations having a higher prealbumin content. An original method will be described to isolate the component PA, from serum and urine. The properties of the preparations will be compared in order to show the identity of these fractions. MATERlAL AND METHODS Serum and Urine CollectionBlood was collected after decapitation of male mice from the BALB/cf and C5'bl/Rij strains. After 16'coagulation the serum was separated by centrifugation for 10 min a t 12,000 xg and stored a t -12". Usually 400 ml of serum, obtained by killing 800 mice, was collected for a preparation. Urine was collected in tubes after a slight massage of the bladder region. Isolation of Prealburnin from SerumThe fractionation was carried out a t 2-4". To 400 rnl of serum were added 30 g of sodium chloride and then dropwise one volume of 5"/, phenol. After centrifugation for 10min a t 31,COOxg the supernatant was collected and dialysed for 48 h against distilled water, then concentrated by freeze-drying to a volume of 2 ml and submitted to preparative starch gel electrophoresis.After migration under the conditions described for ana...
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