Dear Ammar,

if cycle arrest occurs in G0/G1, the possible mechanism  are apoptosis and Proliferation. You need to think about what is most likely the enzyme in both mechanisms.

good luck

Accumulation of cells in G0/G1 (cell arrest) is due to apoptotic mechanism. However to distinguish between intrinsic and extrensic pathways you need to measure caspases enzymes activity ( casp 3, 7, 8, 9) as well as detection of BCl 2 family proteins. Also as an indicator for apoptosis mechanisms, you can detect the expression of the cyclin-dependent kinase inhibitor (p21 protein).

Good luck

This can be useful:

http://www.abcam.com/cell-cycle-pcdkphh3actin-wb-cocktail-ab136810.html

also see: https://www.researchgate.net/post/Any_suggestions_on_markers_for_cell_cycle_arrest_eg_G1_arrest