TISSUE SPECIFICATION AND INTRACELLULAR-DISTRIBUTION OF ACTIN ISOFORMSIN VICIA-FABA L

Two dimensional gel electrophoresis of total cell protein extracts fro m not expanded, and primary leaves, petioles, and roots of Vicia faba resulted in four actin isoforms at 43 kDa with pi values from 5.9 to 6 .05. In contrast to root extracts, in all leaf extracts an additional immunoreactive polypeptide with a molecular mass of 51 kDa and pi 5.75 was detected. This polypeptide was present in high amount in protein extracts of purified chloroplasts, whereas no actin isoform at 43 kDa could be demonstrated. Compared to the tissue extracts, two actin isof orms at 43 kDa with pi values of 5.9 and 6.0 were enriched, when purif ied plasma membranes and the membranous fraction of vacuoles were anal ysed. In contrast, the soluble protein fraction of the plasma membrane preparation contained only two isoactins with pi values of 5.95 and 6 .05 and a molecular mass of 43 kDa. These results indicate, that the f our actin isoforms at 43 kDa detected in all examined tissues of V. fa ba fulfill different functions at specific intracellular compartments, for example, the anchorage of actin microfilaments to membranes.