Related Experiment Videos
Membrane-associated sialidase of rat liver and its decrease in hepatomas
Abstract:
Using the particulate fraction of tissue homogenate, plasma membrane-associated sialidase was assayed at pH 4.5 with bovine brain mixed gangliosides as the substrate. The activity was lower in rat hepatoma induced by 3'-methyl-4-dimethylaminoazobenzene (MeDAB) and transplantable AH-109A rat hepatoma than in normal rat liver. The enzyme was almost quantitatively solubilized from liver particulate fraction by using 0.5% (w/v) sodium deoxycholate plus 0.2% (w/v) Triton X-100. When chromatographed on DEAE-cellulose, the solubilized activity emerged as a single peak. The enzyme thus obtained was maximally active at pH 4.5, and readily hydrolyzed mixed gangliosides but was less active toward 4-methylumbelliferyl-alpha-N-acetylneuraminic acid, 3'-sialyllactose and fetuin. The corresponding enzyme from MeDAB-induced hepatoma was indistinguishable from the liver enzyme in terms of ease of solubilization, pH-activity relationship, chromatographic behavior and substrate preference. It therefore appears that the plasma membrane-associated sialidase of hepatomas differs from that of liver only in the tissue level of activity.
Insights
Plasma membrane-associated sialidase activity is lower in rat hepatomas compared to normal liver tissue. This study found the enzyme
Area of Science:
- Biochemistry
- Enzymology
- Cancer Research
Background:
- Plasma membrane-associated sialidases are enzymes involved in cell surface glycoconjugate metabolism.
- Alterations in sialidase activity have been implicated in various pathological conditions, including cancer.
- Hepatoma, a form of liver cancer, presents a significant health challenge, necessitating research into its underlying molecular mechanisms.
Purpose of the Study:
- To characterize the plasma membrane-associated sialidase in normal rat liver and chemically induced or transplantable rat hepatomas.
- To compare the biochemical properties and substrate specificities of sialidase from normal liver and hepatoma tissues.
- To investigate potential differences in sialidase activity levels between normal liver and hepatoma.
Main Methods:
- Assaying plasma membrane-associated sialidase activity at pH 4.5 using bovine brain mixed gangliosides as substrate.
- Solubilizing the enzyme from particulate fractions using sodium deoxycholate and Triton X-100.
- Chromatographing the solubilized enzyme on DEAE-cellulose to assess its homogeneity and behavior.
- Evaluating substrate preference using various sialidase substrates, including 4-methylumbelliferyl-alpha-N-acetylneuraminic acid, 3'-sialyllactose, and fetuin.
Main Results:
- Plasma membrane-associated sialidase activity was found to be lower in both 3'-methyl-4-dimethylaminoazobenzene (MeDAB)-induced and AH-109A transplantable rat hepatomas compared to normal rat liver.
- The enzyme was efficiently solubilized from liver particulate fractions using a combination of sodium deoxycholate and Triton X-100.
- DEAE-cellulose chromatography revealed a single peak of solubilized sialidase activity, indicating enzyme homogeneity.
- The purified enzyme exhibited optimal activity at pH 4.5 and preferentially hydrolyzed mixed gangliosides over other tested substrates.
- Sialidase from MeDAB-induced hepatoma was biochemically indistinguishable from the liver enzyme in terms of solubilization, pH optimum, chromatographic behavior, and substrate specificity.
Conclusions:
- The plasma membrane-associated sialidase in rat hepatomas is biochemically similar to that found in normal rat liver.
- The primary difference observed between hepatoma and liver sialidase lies in the overall activity level within the tissue.
- These findings suggest that altered expression or regulation of an otherwise similar sialidase enzyme may contribute to hepatoma development.