hydroxyapatite column

[r94223035 from ntu.edu.tw]

Hello all,
I am attempting to purify a subunit(gamma subunit pI=5.81) from  
chloroplast ATP synthase. I've tried to purify it accroding to this  
protocol:
first buffer contains 15mM sodium phosphate(pH 7.0),1mM ATP,0.5mM  
MgCl2, and 4M urea. The alpha(pI=5.16) and beta(pI=5.45) subunits were  
washed by this buffer. Then, the column was washed 15mM sodium  
phosphate(pH 7.0)followed by 200mM sodium phosphate(pH 7.0). The gamma  
subunit was eluted by washing the column with the solution containing  
4M urea and 300mM sodium phosphate(pH 7.0). But alpha and beta  
subunits cannot be washed by first buffer. They are washed through the  
column with gamma subunit. What'S wrong with the protocol? How can I  
correct it? And why did he add ATP to the first buffer? ATP will  
interfere the signal when I detect protein in which fractions by  
UV-VIS. How can I avoid the problem?

Help please

Wu.