Without knowing more details, it is hard to respond, but let me give it a try:

The solubility of amino acids is largely dependent on the pH of your solution, and maybe much higher in acid or alkaline solutions than in water. For reference on Tyrosine, see this paper:

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2140676/pdf/747.pdf

I don't know what pH your medium has, but that might be one thing to consider.

Your assay might also require an excess of tyrosine because it is used (i.e.oxidized) during the assay. So, the effective concentration of tyrosine will go down if tyrosinase is present in your bacteria.

Tyrosine is an aromatic amino acid and its solubility in water does not change very much with pH (its stable between 3,5 and 7,5 if I remember correct).

You could supply more Tyrosine to your media and hope that it gets dissolved as the Tyrosine gets processed by Tyrosinase.

What protocol are you using?

Thanks for your response!

I make a medium for screening of tyrosinase producing bacteria. The medium include glucose 2.0 g/l, L- tyrosine 1.0 g/l, KH2PO4 1.52 g/l, KCl 0.52 g/l,MgSO4.7H2O 0.52 g/l, CuNO3.3H2O 0.001 g/l, ZnSO4.7H2O 0.001 g/l, FeSO4.7H2O 0.001g/l adjusted to pH 7. My problem is that I couldn’t dissolved tyrosine in the medium considering its solubility. Even , boiled water for dissolving tyrosine wasn't successful too. what is your suggestion about this ?

I can not use HCl , because it caused to precipitate the salts in the medium

Hi

May i know the amount of tyrosine (in gm) you practically tested for the solubility.

@Mohammed: You don't have to test it, you can simply get this out of standard tables or even the Wikipedia. Tyrosine has a very low solubility in water.

I've solved tyrosine separately with increased temperature and pH simultaneously.

Where can we find tyrosinase sol