Acid ribonuclease from HeLa cell lysosomes.

Area of Science:

• Biochemistry
• Molecular Biology
• Cell Biology

Background:

• Lysosomes contain enzymes crucial for cellular degradation.
• Ribonucleases (RNases) play key roles in RNA metabolism and turnover.
• Characterizing lysosomal enzymes provides insight into cellular processes.

Purpose of the Study:

• To purify and characterize an acid ribonuclease from HeLa cell lysosomes.
• To determine the enzyme's specific activity, substrate preference, and optimal conditions.
• To investigate the enzyme's biochemical properties and potential role in RNA degradation.

Main Methods:

• Purification of acid ribonuclease from HeLa cell lysosomes.
• Assays for RNase, DNase, phosphodiesterase, and phosphatase activity.
• Characterization of enzyme properties including isoelectric point, pH optimum, and cation requirements.
• Binding studies with Con A-agarose to assess glycoprotein nature.

Main Results:

• The purified acid ribonuclease exhibited significantly higher specific activity in lysosomes compared to other cellular fractions.
• The enzyme showed no DNase, phosphodiesterase, or phosphatase activity, and was specific for acid RNase activity.
• It was identified as a glycoprotein with a low isoelectric point (pH 3.0-3.5) and optimal activity at pH 5.0-5.5.
• Enzyme activity was independent of divalent cations but stimulated by monovalent cations, and inhibited by Cu2+ and Hg2+.
• The enzyme preferentially degraded rRNA over tRNA and poly(U), producing oligonucleotides with 3'-phosphate ends.

Conclusions:

• A distinct acid ribonuclease was purified from HeLa cell lysosomes, demonstrating high catalytic efficiency.
• The enzyme's properties suggest it is a glycoprotein involved in lysosomal RNA degradation.
• Similar enzymes may exist in other cell types, like L-cells, indicating conserved functions.