Properties of beta-glucuronidase activity in human synovial fluid

The purpose of the present study was to evaluate the properties of beta-glucuronidase (EC 3.2.1.31) in human synovial fluid. It was shown to have a pH requirement of 5.0 and a KM value of about 8.0 - 10(-3) M using phenolphthalein beta-glucuronide as the substrate. At low substrate concentration an endogenous inhibitor is demonstrable. The inhibition is of the competitive type and is removed by proteolytic digestion of synovial fluid, whereas hyaluronidase digestion and addition either of Triton X-100 or of various salts to the assay mixture, are ineffective. The possibility that the inhibitor is a protein from serum is discussed.