The catalytic transformations of 2-methylpentane (2MP), and methylcyclopentane (MCP), over Co/NaY, Pt-Co/NaY, Pt-Co/Al2O3 and NaY samples have been investigated. Co/NaY was found to be an excellent isomerization catalyst, in contrast to Co/Al2O3 on which the main route was observed to be cracking. This is attributed to the difference in cobalt reducibility over the two supports. The use of C-13-labelled 2-methyl pentanes made the elucidation of the mechanism of isomerization on these samples possible. A cyclic mechanism (CM) operates only on metal particles, while for both metal particles and support, a bond shift mechanism (BS) is the main route for isomerisation. On Pt-Co/NaY samples, the contribution of the cyclic mechanism to isomerisation relative to isomerisation by bond shift route is significantly enhanced on the catalysts with cobalt loading higher than 22 at.%. The results are discussed in terms of small metal particles inserted into NaY supercage and the enhanced reduction of cobalt ions.