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M Dobrota

Publications and source records attributed to M Dobrota.

At least 37 records · Page 2Linked to original sources
PubMed1987

Changes in lysosome populations in the rat kidney cortex induced by passive Heymann glomerulonephritis.

Acute passive Heymann glomerulonephritis in rats induced heavy proteinuria and highly increased urinary activity of N-acetyl-beta-D-glucosaminidase, acid beta-galactosidase and acid phosphatase. The cortical activity of these acid hydrolases was increased essentially in the large lysosomes as demonstrated by subfractionation of the lysosome-rich mitochondrial-lysosomal fraction, by rate zonal centrifugation. Banding density of small lysosomes shifted or reduced to slightly lower value (1.225 g/ml), which is between the banding densities of small 'light' (1.20 g/ml) and small 'dense' lysosomes (1.235 g/ml) in normal rat kidney cortex. Labelled protein reabsorbed in the proximal tubule is recovered in these populations of small lysosomes as well as in the large lysosomes or 'protein droplets'. Glomerulonephritis also induced a new population of small 'light' lysosomes (density 1.185-1.195 g/ml) enriched in cathepsin D. The previously demonstrated morphological, biochemical, and physiological heterogeneity of renal lysosomes was confirmed and emphasized in the kidney cortex of glomerulonephritic rats. The main changes in the lysosomal populations appear to reflect the increased protein reabsorption as confirmed by the proteinuria.

Acetylglucosaminidase↗
PubMed1986

The lysosomal distribution of cathepsin B in the rat kidney cortex.

Subcellular distribution of cathepsin B following subfractionation of the kidney cortex mitochondrial/lysosomal fraction by rate sedimentation indicates that this enzyme is mainly associated with the large, fast sedimenting lysosomes (protein droplets). A small proportion of cathepsin B is also present in the small lysosomes which cosediment with mitochondria, peroxisomes, and brush border and other large membrane vesicles. Amongst this broad spectrum of small lysosomes the distribution of cathepsin B, together with other acid hydrolases is associated with the more rapidly sedimenting lysosomes whilst cathepsin D differs in being associated with the slowest sedimenting lysosomes. Equilibrium banding in sucrose gradients shows the large lysosomes band at a density of 1.235 g/ml and that the small lysosomes have two distinct populations at densities 1.20 and 1.235 g/ml. Cathepsin B (and also cathepsin D and acid ribonuclease) appears to be associated only with lysosomes of high density. The various other acid hydrolases assayed are found in all the lysosomal populations. Small and large lysosomes of high density are very rich in a number of proteinases and therefore most probably represent lysosomal populations involved in the catabolism of proteins taken up from the glomerular filtrate.

Animals↗
PubMed1980

Distribution of secretory component in hepatocytes and its mode of transfer into bile.

Immunoglobin A in bile and other external secretions is mostly bound to a glycoprotein known as secretory component. This glycoprotein is not synthesized by the same cells as immunoglobulin A and is not found in blood. We now report the mechanism by which secretory component reaches the bile and describe its function in immunoglobulin A transport across the hepatocyte. Fractionation of rat liver homogenates by zonal centrifugation was followed by measurement of the amounts of secretory component in the various fractions by rocket immunoelectrophoresis. Secretory component was found in two fractions. One of these was identified as containing Golgi vesicles from its isopycnic density and appearance in the electron microscope; the other contained principally fragments of the plasma membrane of the sinusoidal face of the hepatocyte, as shown by its particle size and content of marker enzymes. Only the latter fraction bound (125)I-labelled immunoglobulin A added in vitro. At 5min after intravenous injection of [(14)C]fucose, the secretory component in the Golgi fraction was labelled, but not that in the plasma membrane. The secretory component in the sinusoidal plasma membrane did, however, become labelled before the first labelled secretory component appeared in bile, about 30min after injection. We suggest that fucose is added to the newly synthesized secretory component in the Golgi apparatus. The secretory component then passes, with the other newly secreted glycoproteins, to the sinusoidal plasma membrane. There it remains bound but exposed to the blood and able to bind any polymeric immunoglobulin A present in serum. The secretory component then moves across the hepatocyte to the bile-canalicular face in association with the endocytic-shuttle vesicles which carry immunoglobulin A. Hence there is a lag before newly synthesized secretory component appears in bile.

Animals↗
PubMed1979

Endocytic vesicles in liver carry polymeric IgA from serum to bile.

The distributions both of endogenous IgA and of injected 125I-labelled IgA were determined amongst the components of a liver homogenate. Rate zonal sedimentation, under conditions where separation was principally determined by particle size, showed that IgA was tightly bound to material which sedimented in the size range of the larger endoplasmic reticulum fragments. Further fractionation of the components within this size range according to their densities, by isopycnic centrifugation, showed that the IgA was associated with small vesicles with a density range of 1.12--1.17 g/ml, quite distinct from endoplasmic reticulum fragments. We therefore conclude that the IgA is present in liver cells in a distinct class of vesicles, which are, presumably, responsible for the transport of IgA from blood to bile.

Animals↗
PubMed1979

Apparent heterogeneity of hepatic lysosomes due to membrane-bound acid phosphatase.

Hepatic lysosomes have been fractionated by rate sedimentation and by isopycnic banding. In all experiments, the distribution of acid phosphatase differed from that of the other lysosomal enzymes. Evidence is presented that this difference is due not to the separation of lysosomes from different cell types, but simply reflects the membrane location of a part of the acid phosphatase.

Acid Phosphatase↗
PubMed1978

Sources of the proteins of rat bile.

The protein composition of rat bile has been studied systematically using two-dimensional agarose-polyacrylamide gel electrophoresis, with or without prior absorption by immobilised antisera, and by crossed immunoelectrophoresis. Sixteen bile proteins were distinguished. Of these, thirteen are immunologically identical to proteins present in rat serum and only one is identical to a protein present in rat liver plasma membrane but not in rat serum. Of the remaining two proteins, one is bile lipoprotein and the other has many of the properties of immunoglobulin A secretory component. The serum-related proteins in rat bile fall into two distinct groups. In the first group are immunoglobulin A and an alpha2-globulin. These proteins are major constituents of bile but only minor constituents of serum. In the second group are albumin and some other major serum proteins which are found in bile at concentrations less than 1% of their concentrations in serum. The relative proportions of these proteins in bile appear to differ from their proportions in serum. It therefore appears that, although the majority of bile proteins are derived from serum, there cannot be direct leakage of serum into bile. Examination of the proteins contained within liver lysosomes indicates that, although discharge of lysosomal contents at the bile canalicular face of the hepatocyte may contribute to the bile proteins, an additional mechanism, with a considerable degree of selectivity, must also be involved in the transport of proteins from serum to bile.

Animals↗
PubMed1974

Heterogeneous distribution of enzymes among plasma-membrane fragments sedimenting with the microsomal fraction of rat liver.

Plasma-membrane fragments recovered in the microsomal fraction of rat liver homogenates were shown to be heterogeneous in density. It was demonstrated that 5'-nucleotidase, the most commonly used plasma-membrane marker, is concentrated in the lightest subfraction. Two of the published procedures for the isolation of plasma-membrane fragments from the microsomal fraction (Touster et al., 1970; Hinton et al., 1971) are shown to give products which are not representative of all the plasma-membrane fragments of microsomal size, and it is argued that a third procedure (House & Weidemann, 1970) is likely to give a similar product.

Adenine Nucleotides↗