We note that the recent direct measurement of the top quark mass at 173.3±5.6(stat)±6.2(syst) by D0 collaboration severely constrains the
theoretically attractive infra-red fixed point scenario of the top quark Yukawa
coupling in supersymmetric GUTs. For one-step unified models the above
mentioned measurement bounds the arbitrary but experimentally determinable
parameter tanβ to the range 1.3≤tanβ≤2.1. Further
crunch on the top quark mass may determine tanβ even more accurately
within the fixed point scenario. On the other hand an experimental value of
tanβ>2.1 will rule out the fixed point scenario bounding
ht2(MX)/4π to 0.022 from above.Comment: 7 pages, Latex with epsf style, 1 figure, captions.st