Comparison of D-beta-hydroxybutyrate dehydrogenase from rat liver and brain mitochondria

The properties of D-beta-hydroxybutyrate dehydrogenase (BDH) from rat liver and brain mitochondria were compared to determine if isozymes of this enzyme exist in these tissues. The BDHs from these tissues behaved similarly during the purification process. The enzymes were indistinguishable by sodium dodecyl sulfate-polyacrylamide or acid-urea-polyacrylamide gel electrophoresis and they had identical isoelectric points. The BDHs from rat liver and brain were also quite similar in functional parameters determined by kinetic analysis and phospholipid activation of apo-BDH (i.e., the lipid-free enzyme). Antiserum against rat liver BDH inhibited both enzymes to an equivalent extent in a titration assay. The enzymes had similar patterns of peptide mapping by partial digestion with Staphylococcus aureus V8 protease, followed by immunoblotting using antiserum against the liver enzyme. These results suggest that the BDHs in rat liver and brain are very similar and possibly identical.

Regulation of succinyl coenzyme A:acetoacetyl coenzyme A transferase in rat hepatoma cell lines

The regulation of succinyl-CoA:acetoacetyl-CoA transferase (CoA transferase) has been studied in 8 rat hepatoma cell lines. Compared with normal rat hepatocytes, which have almost nondetectable activity of the enzyme, the hepatoma cell lines have a wide range of expression of CoA transferase activity, from as low as 45 nmol/min/mg to as high as 960 nmol/min/mg. Western blotting showed that the different levels of CoA transferase activity were due to differing amounts of the enzyme in the cells. This was further attributed to the varying amounts of the enzyme synthesized in the cells as monitored by L-[35S]methionine labeling followed by immunoprecipitation. To study further the differential expression of CoA transferase in the hepatoma cell lines, the relative quantity of functional CoA-transferase mRNA in the cells was measured by in vitro translation. The results showed that the levels of functional CoA transferase mRNA detected were consistent with the differences in the enzyme activity in the cells. Since CoA transferase is the key enzyme responsible for the utilization of ketone bodies as an alternative energy source, the expression of CoA transferase in hepatoma cells may play a role in energy production.

Purification of D-beta-hydroxybutyrate dehydrogenase from rat brain

D-beta-Hydroxybutyrate dehydrogenase (BDH), a lipid-requiring enzyme, has been purified to homogeneity from rat brain using a new improved method. The purified rat brain BDH has a subunit molecular mass of 31 kilodaltons on sodium dodecyl sulphate-polyacrylamide gel electrophoresis. The apoenzyme, i.e., the enzyme devoid of phospholipid, has no activity, but can be activated by phospholipid to a specific activity of 125 mumol/(min.mg). This is 625-fold greater than the activity in the mitochondrial fraction. The new purification procedure involves chromatography using a quaternary amine Sepharose resin followed by a sulphonate Sepharose resin, and eliminates the need for glass bead adsorption chromatography.

Effects of rhodamine 6G on the mitochondrial ultrastructure of mouse spermatocytes

Effects of rhodamine 6G on spermatocyte mitochondria were assessed in BALB/c mice in vivo. Four groups of mice were given rhodamine 6G doses of 0.0, 0.3 and 0.5 and 0.8 mg.kg-1.d-1 i.p. for 5 days. On the 5th day after the last day of dye administration, the mice were killed and testicular tissue was prepared for electron microscopy. Exposure to rhodamine 6G resulted in dose-dependent effects, primarily intracristal expansion of mitochondria.

Genomic structure of the human proliferating cell nucleolar protein P120

A gene for human proliferating cell nucleolar protein p120 has been isolated from a human genomic library using p120 cDNA as a probe. The gene spanned 12 kilobase pairs and was composed of 15 exons and 14 introns. Unusual splice junction sequences, (AT) and (AC), instead of (GT) and (AG), respectively, were located at the splice sites for intron F. The 5' flanking region was analyzed for putative cis-acting factor binding sites. The region contained a TATA-like sequence and the CCAAT box. CAT assays indicated that the region -2532 /+ 102 was necessary for transcription. Two specific areas at -1444/-1224 and -537/-278 were shown to be important for transcription. Two "GC" boxes and two "GC"-rich sequences were observed Other sites upstream of these sites were analyzed for homology to other gene control regions.

Developmental regulation of D-beta-hydroxybutyrate dehydrogenase in rat liver and brain

The activities of ketone-metabolizing enzymes in rat brain increase 3- to 5-fold during the suckling period before decreasing to the adult level after weaning. We have observed that a similar developmental pattern also exists for D-beta-hydroxybutyrate dehydrogenase (BDH) in rat liver. Utilizing antibodies prepared against the purified protein we determined that the changes in BDH activities in both brain and liver are due to changes in the amount of BDH in the mitochondria. In vitro translations of isolated RNA followed by immunoprecipitation revealed that the increase in BDH activity and content was correlated with an increase in the level of functional BDH-mRNA in both liver and brain.

Regulation of D-beta-hydroxybutyrate dehydrogenase in rat hepatoma cell lines

Quantitation of D-beta-hydroxybutyrate dehydrogenase (BDH) in normal rat hepatocytes was compared with that in two rat hepatoma cell lines, H4-II-EC3 and RLT-3C. BDH activity in normal rat hepatocyte mitochondria was 321 nmol/min/mg, which was greatly reduced to 10.7 nmol/min/mg and 1.7 nmol/min/mg in H4-II-EC3 and RLT-3C cell mitochondria, respectively. The cell growth rate and L-[35S]methionine incorporation rate showed that RLT-3C cells had the highest growth rate (32.4-h doubling time) and the fastest protein biosynthesis rate (2.65 x 10(5) cpm/min/10(6) cells). The H4-II-EC3 cell line grew more slowly (48.5-h doubling time) and had lower protein biosynthesis rate (1.46 x 10(5) cpm/min/10(6) cells). The protein synthesis rate in hepatocytes was 1.25 x 10(5) cpm/min/10(6) cells. These results suggest that there is a reciprocal correlation between BDH activity and cell growth and protein synthesis rates. Immunochemical quantitation of BDH showed the amount of BDH in H4-II-EC3 and RLT-3C cells was about 4.8 and 0.5% of that in normal rat hepatocytes, respectively. Quantitation of BDH by biosynthesis indicated that BDH content in H4-II-EC3 cells and RLT-3C cells was 9.3 and 4.0% of that of normal hepatocytes, respectively. Precursor BDH synthesized by in vitro translation primed with RNA of H4-II-EC3 cells or RLT-3C cells was 3.0 and 1.1% of that translated from normal rat hepatocyte RNA. These results suggest that the decrease in BDH content in hepatoma cells results from a decrease in functional BDH-mRNA. The coupling of a decrease in BDH activity with an increase in activity of succinyl-CoA: acetoacetyl-CoA transferase in hepatoma cells may play a role in generating additional energy required for the rapid growth of tumor cells.