Localization of enzymes in Ureaplasma urealyticum (T-strain mycoplasma)

Abstract

U. urealyticum cells were lysed by osmotic shock or by digitonin. The membrane fraction contained 4-10 times as much protein as the cytoplasmic fraction. These values are in large excess of those reported for classical mycoplasmas, suggesting that the Ureaplasma membrane fraction was heavily contaminated with proteins derived from the growth medium. The U. urealyticum urease activity was localized in the cytoplasmic fraction, but the ATPase activity was localized in the membrane fraction. Significant urease activity could be detected also in nonviable cells. Urea, at concentrations > 0.25 M, was mycoplasmastatic to Acholeplasma laidlawii, Mycoplasma hominis and U. urealyticum, so that the Ureaplasma urease did not afford preferential protection against urea toxicity. The intracellular localization of the urease would be expected to release NH3 from urea in the cytoplasm. The NH3 will take up protons to become NH4+. The intracellular NH4+ probably plays a role in proton elimination or acid-base balance, which might be coupled to an energy producing ion gradient and/or transport mechanisms.