Non-competitive inhibition of honeybee haemolymph pNP-alpha-D-glucosidase by chloramphenicol.--A study in vitro.

The haemolymph pNP-alpha-D-glucosidase activity of emerging worker bees shows a tendency towards negative cooperativity (n = 0.92). The relation between initial velocity and enzyme concentration is not exactly linear (bilogarithmic exponent = 0.91). Between 25 degrees and 31 degrees C, the activation energy, EA = 38.2 kJ/mol. Chloramphenicol administered in vitro decreases the maximum velocity and re-establishes pure Michaelian kinetics (n congruent 1.0). The Hill coefficient for the binding of chloramphenicol to the enzyme, ni = 1.13; the values of Ki = 20.7 mM, K'i = 17.3 mM, and I50 = 17.6 mM are not significantly different from one another. These data indicate that inhibition by chloramphenicol is of the pure, non-competitive type.