Chain-length dependence of the kinetics of the hyaluronan hydrolysis catalyzed by bovine testicular hyaluronidase.

Hyaluronan (HA) has various biological functions that are strongly dependent on its chain length. In some cases, as in inflammation and angiogenesis, long and short chain-size HA effects are antagonistic. HA hydrolysis catalyzed by hyaluronidase (HAase) is believed to be involved in the control of the balance between longer and shorter HA chains. Our studies of native HA hydrolysis catalyzed by bovine testicular HAase have suggested that the kinetic parameters depend on the chain size. We thus used HA fragments with a molar mass ranging from 8x10(2) g mol(-1) to 2.5x10(5) g mol(-1) and native HA to study the influence of the chain length of HA on the kinetics of its HAase-catalyzed hydrolysis. The initial hydrolysis rate strongly varied with HA chain length. According to the Km and Vm/Km values, the ability of HA chains to form an efficient enzyme-substrate complex is maximum for HA molar masses ranging from 3x10(3) to 2x10(4) g mol(-1). Shorter HA chains seem to be too short to form a stable complex and longer HA chains encounter difficulties in forming a complex, probably because of steric hindrance. The hydrolysis Vm values strongly suggest that as the chain length decreases the HAase increasingly catalyses transglycosylation rather than hydrolysis. Finally, two HA chain populations, corresponding to HA chain molar masses lower and higher than approximately 2x10(4) g mol(-1), are identified and related to the bi-exponential character of the model we have previously proposed to fit the experimental points of the kinetic curves.