Hi AnjaliKrsih,
It depends on how big difference are there between all these isozymes. If they have indeed very similar in size, 1D-PAGE with regular running condition is almost impossible to separate them. While increasing the electrophoresis time, you are indeed also increase the resolving power of molecules/proteins with very similar size. I suspect, letting the gels run extra-long might be the only way to go for 1D-PAGE separation.
Good luck.