Nucleotidase activities of human peripheral lymphocytes

Area of Science:

• Biochemistry
• Cell Biology
• Immunology

Background:

• B lymphoblastic cell lines show resistance to 2'-deoxyadenosine and adenosine deaminase inhibitors.
• This resistance is linked to enhanced dephosphorylation of 2'-deoxyadenosine nucleotides, preventing toxic metabolite buildup.

Purpose of the Study:

• To investigate the 2'-deoxynucleoside 5'-monophosphate dephosphorylating activities in human peripheral lymphocytes.
• To characterize the properties of these nucleotide-dephosphorylating enzymes.

Main Methods:

• Analysis of nucleotide 5'-monophosphate nucleotidase activities in human peripheral lymphocytes.
• Characterization of enzymes based on pH optimum, substrate preference, Mg2+ requirement, inhibitors, and molecular weights.

Main Results:

• Identified at least three distinct nucleotide 5'-monophosphate nucleotidases in peripheral lymphocytes.
• Two cytosolic enzymes were characterized: one with acidic pH optimum and broad substrate specificity for dAMP, and another requiring Mg2+ with a preference for purine and pyrimidine deoxynucleosides.
• A third enzyme, ecto 5'-nucleotidase, was associated with the cell membrane, showing higher activity in B lymphocytes, while cytosolic nucleotidase activity was similar in T and B lymphocytes.

Conclusions:

• Human peripheral lymphocytes possess a complex system of nucleotidases for deoxynucleotide metabolism.
• Cytosolic nucleotidases play a significant role, with distinct characteristics and substrate preferences.
• Differential expression of ecto 5'-nucleotidase in B lymphocytes may contribute to their metabolic profile.