Proton NMR spectroscopic studies of dipeptidase in human erythrocytes

In studies on human erythrocyte metabolism in situ, high resolution (400 MHz)¹H spin-echo NMR spectroscopy was used to follow the time dependence of hydrolysis of glycylglycine and L-cysteinylglycine in intact cells and their lysates. The concentration dependence of the hydrolysis of L-cysteinylglycine was described by a rectangular hyperbola with K_m, 3.5 ± 0.6 mmol/llysate and V_max, 64.2 ± 3.2 mmol/llysate/h. We demonstrated that glycylglycine readily enters the erythrocyte and we introduce a means of analysing the data from the coupled reaction sequence; the sequence consists of transport followed by enzyme catalysed hydrolysis.