Alanine Aminotransferase and Aspartate Aminotransferase in Leishmania tarentolae1

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Abstract
SYNOPSIS. Culture stages (promastigotes) of Leishmania tarentolae were tested for alanine aminotransferase (E.C.2.6.1.2) and aspartate aminotransferase (E.C.2.6.1.1.). Neither enzyme was detected in crude cell extracts. After starch block electrophoresis, however, both transaminase activities were found in proteins migrating toward the anode. Only one species of each enzyme was found. Using coupled enzyme assay systems, the following physical and kinetic properties were seen: 1) aspartate aminotransferase was inhibited by α‐ketoglutarate concentrations above 1.68 × 10−2 M and alanine aminotransferase was inhibited by concentrations higher than 1.34 × 10−2 M; 2) the Michaelis constant (Km[α‐ketoglutarate]) was 5.4 × 10−4 M for aspartate aminotransferase and 3.0 × 10−4 M for alanine aminotransferase; 3) maximum activity was found at ˜pH 8.5 (broad range between pH 7.75–9.0) for aspartate aminotransferase whereas maximum activity for alanine aminotransferase was ˜pH 7.2 (range between pH 7.0–7.5); 4) both enzymes lost half of their activity after 4 days at 8 C; 5) aspartate aminotransferase was most active at 35 C and completely inactivated at 59.5 C, alanine aminotransferase exhibited maximum activity at 29.5 C and was completely inactivated at 61 C; and 6) neither enzyme showed enhanced activity with added pyridoxal phosphate.

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