Per the DB2 Manual, the LIMITKEY is stored in INTERNAL-format in the SYSINDEXPART table:
"LIMITKEY VARCHAR(512) NOT NULL WITH DEFAULT FOR BIT DATA
The high value of the limit key of the partition in an internal format. An empty string if the index is not partitioned or for a data-partitioned secondary index (DPSI). If any column of the key has a field procedure, the internal format is the encoded form of the value.""
To see the EXTERNAL-format, see LIMITKEY in the SYSTABLEPART table:
"LIMITKEY VARCHAR(765) NOT NULL
The high value of the partition in external format. If the table space was converted from index-controlled partitioning to table-controlled partitioning, the value is the highest possible value for an ascending key, or the lowest possible value for a descending key. If the table space is not partitioned, the value is an empty string."