COMPARISON OF PLASMA-MEMBRANE H-ATPASE ACTIVITY IN VESICLES OBTAINED FROM DRY AND HYDRATED MAIZE EMBRYOS()

ATP hydrolysis from H+-ATPase of plasma membrane was measured in vesic les from maize embryos imbibed at times between 0 and 5 h. The activit y had a maximum at 2 h of imbibition. In order to detect whether the e nzyme had the same characteristics through the first 5 h of imbibition , vanadate and lysophophatydilcholine sensitivities, as well as trypsi n, pH and temperature effects on the activity of the H+-ATPase from pl asma membrane vesicles isolated from embryos imbibed at 0 or 5 h were studied. The results indicate that the activity expressed at 0 h is ve ry different from the activity at 5 h. The activity from embryos imbib ed for 5 h was less sensitive to vanadate, trypsin and lysophosphatidy lcholine, more sensitive to denaturing temperatures and with a broader pH dependence, as compared to the activity from embryos that were not imbibed. When vanadate-sensitive ATPase activity was purified by anio n exchange chromatography, the peaks obtained from the 0 and 5 h imbib ed embryos were different and non-overlapping. These data could be int erpreted in terms of different enzyme structures from dry and imbibed embryos due to either different primary structures or covalent modific ations, or differences in membrane vicinities. (C) 1998 Elsevier Scien ce B.V. All rights reserved.