Non-linear fitting in matlab

I have x and y data and would like to make a nonlinear fitting between them according to this equation,

y= [C(x/x_m)]/[1+D(x/x_m)]^(5/3)

The measured values are x and y and the best fit line should give me the values of C,D and x_m. Actually this is a spectral fitting and x_m denotes the point where y attains its maximum. I would be very grateful if any expert can help me out on this.

[KSSV]

what you have done so far?

[subharthi chowdhuri]

Thank you very much for your reply. I am bit confused about the x_m part. x_m is the point where y attains the maxima and it is already included in the fit equation. So how can that be handled. Like if it was only (C*x)/(1+Dx)^(5/3) it could have been solved by using lsqcurvefit. Could you please help me out further?

[Torsten]

x_m should be the x-value where

C*x/(1+D*x)^(5/3)

or where

C*(x/x_m)/(1+D*(x/x_m))^(5/3)

attains its maximum ?

Best wishes

Torsten.