Sugar beet arginase extraction

[P.Longdon]

Dear All,
      I have just started my work experience placement as a Research 
Assistant and will be looking at the effects of nitrogen, sulphur and
potassium on the free amino acid content of sugar beet.
  I would also like to do assays on arginase activity, and this is really
the bit for which I could do with some tips: how would I go about extracting
and/or purifying this enzyme (a crude extract is really all I'd need) from
the leaves of the plant?

		Yours,
			Pete.