Aminopeptidase activity associated with purified murine leukaemia viruses

Area of Science:

• Virology
• Enzymology
• Biochemistry

Background:

• Murine leukaemia viruses (MuLV) are retroviruses implicated in various leukaemias.
• The enzymatic composition of MuLV virions is not fully characterized.
• Aminopeptidases (AP) are enzymes that cleave amino acids from peptide N-termini.

Purpose of the Study:

• To investigate the presence and nature of aminopeptidase activity in purified MuLV preparations.
• To determine if AP activity is an intrinsic viral component or a contaminant.

Main Methods:

• Extensive purification of Rauscher leukaemia virus (RLV) using rate and density gradient centrifugation.
• Assay of aminopeptidase activity in purified RLV, Moloney leukaemia virus, and Gross leukaemia virus.
• Comparison of viral AP activity with purified hog kidney aminopeptidase M and leucine aminopeptidase.
• Characterization of pH optimum and substrate specificity of the viral AP activity.

Main Results:

• Purified RLV exhibited significant aminopeptidase activity, approximately 0.005 times that of purified hog kidney aminopeptidase M.
• Similar AP activity was detected in purified Moloney and Gross leukaemia viruses, but not in uninfected cell fractions.
• AP activity remained consistent when serum was replaced with bovine serum albumin in cell culture media, suggesting it is not serum-derived.
• Characterization revealed the MuLV AP activity is similar to, yet distinct from, known hog kidney aminopeptidases.

Conclusions:

• Murine leukaemia viruses (MuLV) possess a tightly bound, intrinsic aminopeptidase activity.
• This viral AP activity is a minor component of the virion preparation.
• The identified MuLV aminopeptidase differs from characterized host cell or serum enzymes.