I recommend that you upload your list of mnemonics to the UniProt Batch retrieve/IDmapping tool at https://www.uniprot.org/uploadlists
This will return the list of accession numbers - click on "Downloads" to obtain either the mapping table or the list of UniProtKB ACs. These are more widely used in other databases.
The UniProtKB/Swiss-Prot entry name consists of up to 11 uppercase alphanumeric characters with a naming convention that can be symbolized as X_Y, where:
X is a mnemonic protein identification code of at most 5 alphanumeric characters;
The mnemonic code 'X' is an abbreviation of the protein/gene name, which does not necessarily correspond to the recommended protein name or to the gene name (https://www.uniprot.org/help/entry_name).
Please don't hesitate to contact the UniProt helpdesk if you have any addtional questions.