As both CATPART and PRT file contain a technical drawing of a part of a product, it should be quite possible to somehow convert it from one to another. The tricky part would be to find a program that exports to PRT, as this file type was used by many programs and it is likely at least some of them had their own unique format. So it would probably be best to use some universal exchange formats.
Convert CATIA part data to CAD 3D part or component.
We found one software available in the database for this conversion.
Microsoft Windows software - convert catpart to prt on Windows
A CAD converter with huge format support
Convert from catpart file format
The table with program actions contains information about what each program is capable of doing with their files. This may be a good pointer for further searches for certain file conversions and help you find the converter you are looking for if our search result is insufficient for you. However, it is far from perfect and may sometimes show results which are not really usable because of the nature of the software handles the files. So a conversion that appears as possible, just because of matched actions, may in fact not be possible.