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Biomedical subjects

J D Judah

Publications and source records attributed to J D Judah.

At least 37 records · Page 2Linked to original sources
PubMed1971

Biosynthesis of rat serum albumin.

1. The labelling of intracellular and extracellular serum albumin was studied in liver slices and in whole rats by using new methods for the purification of the protein. 2. The results suggest that a polypeptide precursor is formed that is converted relatively slowly into serum albumin. 3. The effect of liver cell K(+) has been examined by a double-label method and it is shown that K(+) accelerates the rate of conversion of ;precursor' into albumin. The rate of transit of albumin across the cell membrane appears to be unrelated to the concentration of K(+) within the cell. 4. The time-course of incorporation of radioactive amino acid into albumin follows a sigmoidal mode. There is a pronounced time-lag before label starts to appear in intracellular albumin, and a further time-lag before it appears in extracellular albumin. 5. In slices the sum of intra- and extra-cellular label rises steadily from 30min after the start of labelling with a pulse of labelled leucine or valine and continues to rise for at least another 60min. This occurs whether labelling is stopped by addition of excess of carrier amino acid or with cycloheximide (100mum) or both. 6. The intracellular albumin content remains constant whether slices are maintained with low or normal intracellular K(+) concentrations. 7. Specific radioactivities of intracellular albumin (and fractions thereof) and of extracellular albumin were determined in vitro and in vivo. The results show that the intracellular albumin cannot be a precursor of extracellular albumin, unless a very small compartment is turning over much more rapidly than the bulk of the liver albumin or even of the microsomal albumin.

Animals↗
PubMed1970

Role of liver-cell potassium ions in secretion of serum albumin and lipoproteins.

1. The incorporation of l-[1-(14)C]leucine into the proteins of liver slices and into the serum albumin and lipoproteins transported by these slices was investigated. 2. Transport rates were found to be dependent on the K(+) content of the slices. 3. The effect of K(+) on transport of serum albumin and of serum lipoprotein can be separated from any effect on synthesis by altering K(+) concentrations after inhibition of protein synthesis by cycloheximide or puromycin. 4. The effect of low K(+) concentrations is reversible. 5. There is linear relationship between the K(+) content of the slices and the transport of protein. A simple method is described for maintaining various steady concentrations of K(+) in the liver slices. 6. K(+) may be replaced by Rb(+). Cs(+) is partly effective, but NH(4) (+) and Li(+) are no more effective than Na(+). 7. We found evidence that K(+) content rather than the flux rates of K(+) or Na(+) is important in this effect. 8. These results are probably important in ethionine and carbon tetrachloride poisoning in the rat, and may be significant in liver transplantation.

Animals↗
PubMed1970

Ultrastructural studies on mitochondrial swelling.

Mitochondrial swelling induced by valinomycin, calcium chloride and P(i) was studied after potassium permanganate fixation in suspension. Valinomycin induces a rapid K(+) influx, increase of the matrix space and out-folding of the cristae, with good preservation of the matrix material. This swelling is reversible but the cristae do not completely re-form and have a blebbed appearance. On repeated swelling and contraction cycles there is a gradual loss of matrix material. Calcium chloride and P(i) produce a slow swelling of the matrix space. Shrinkage induced by ATP was partial and not associated with return to the original structure.

Adenosine Triphosphate↗
PubMed1970

Preparation of isolated rat liver mitochondria for electron microscopy.

A comparative study of the fixation of isolated rat liver mitochondria was undertaken. If the criterion is adopted that after processing, the mitochondria should resemble as closely as possible rat liver mitochondria in situ, the procedure found to produce such preservation was that of fixation in suspension in veronal-buffered 2% potassium permanganate. Fixation in osmium tetroxide produced variable results, while mitochondria fixed in glutaraldehyde were contracted. We suggest that in cases where fixation procedures modify the morphological appearance of mitochondria, the significance of such changes must be treated with caution.

Aldehydes↗
PubMedDate not supplied

Secretion and biosynthesis of N-acetyl-beta-D-hexosaminidases by human placental tissues in vitro.

Chorionic villi selectively secrete the B isoenzyme and, to a lesser extent, the A isoenzyme of lysosomal beta-hexosaminidase when incubated in vitro, suggesting that this tissue could contribute to maternal serum beta-hexosaminidase B and A activities in vivo. The results make it unlikely, however, that the placenta is the source of the I2 isoenzyme found in maternal serum. Samples of amnion and term chorion laeve secreted predominantly the B isoenzyme whereas first-trimester chorion laeve secreted the A, B and I2 isoenzymes. Amnion and chorion laeve may, therefore, be a source of the A, B and I2 activities found in amniotic fluid. Chorionic villi supported the cycloheximide-sensitive incorporation of [3H]leucine into immunoreactive beta-hexosaminidase thereby providing direct evidence for enzyme biosynthesis. Newly synthesized beta-hexosaminidase was detectable in the medium only after extended incubation and the secretion of beta-hexosaminidase activity continued at normal rates for several hours in the absence of protein synthesis. These results indicate that enzyme synthesis is not a primary factor in the regulation of enzyme secretion.

Chromatography, DEAE-Cellulose↗