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S-adenosylmethionine: DNA-cytosine 5-methyltransferase from a Novikoff rat hepatoma cell line
Abstract:
Partial purification of DNA methylase from Novikoff rat hepatoma cells is described. Contamination with other proteins persists although the enzyme preparation has a high specific activity and is purified 980-fold over homogenate activity. Evidence suggests, but does not prove, that there may be more than one species of DNA methylase in these cells. The enzyme has two broad pH optima at pH 7.0 and 7.5 and most readily methylates heterologous denatured DNAs although complex reaction kinetics indicate that native DNAs may eventually be methylated to an equal or greater level. The preparation of undermethylated DNA from Novikoff cells is also described. Undermethylated homologous DNA is an 85-fold greater acceptor of methyl groups than fully methylated Novikoff cell DNA. In contrast to other DNA substrates, the enzyme preparation methylates native undermethylated homologous DNA at a 3.5-fold greater than denatured undermethylated homologous DNA.
Insights
Researchers partially purified DNA methylase from Novikoff rat hepatoma cells, finding it prefers denatured DNA but can methylate native DNA. Undermethylated DNA is a significantly better substrate for this DNA methylase.
Area of Science:
- Biochemistry
- Molecular Biology
- Enzymology
Background:
- DNA methylation is a crucial epigenetic mechanism regulating gene expression.
- Understanding DNA methylase enzymes is key to deciphering epigenetic regulation.
- Novikoff rat hepatoma cells provide a model for studying DNA methylation processes.
Purpose of the Study:
- To partially purify DNA methylase from Novikoff rat hepatoma cells.
- To characterize the substrate specificity and kinetic properties of the purified enzyme.
- To investigate the preparation and properties of undermethylated DNA from these cells.
Main Methods:
- Partial purification of DNA methylase using established biochemical techniques.
- Enzyme activity assays to determine specific activity and purification fold.
- Characterization of enzyme kinetics across different pH optima and DNA substrates (native vs. denatured, homologous vs. heterologous, methylated vs. undermethylated).
Main Results:
- A DNA methylase preparation was obtained with 980-fold purification and high specific activity, though still containing protein contaminants.
- The enzyme exhibited broad pH optima around 7.0 and 7.5.
- The enzyme preferentially methylated denatured heterologous DNAs, but native DNAs could eventually be methylated to comparable levels.
- Undermethylated homologous DNA was an 85-fold better methyl group acceptor than fully methylated DNA.
- Native undermethylated homologous DNA was methylated 3.5-fold more efficiently than its denatured counterpart.
Conclusions:
- Evidence suggests the potential existence of multiple DNA methylase species within Novikoff cells.
- The characterized DNA methylase shows complex substrate preferences, favoring denatured DNA but capable of methylating native DNA.
- Undermethylated DNA serves as a highly efficient substrate for this DNA methylase, highlighting its potential role in DNA repair or replication.