A possible alternative route is to use koji.

Sikander and Ul-Haq report:
"mould mycelium of Aspergillus oryzae was used for biochemical conversion of L-tyrosine to L-DOPA" [1]

Aspergillus oryzae, known as koji in Japan:
"is a filamentous fungus (a mold). It is used in Chinese and Japanese cuisine to ferment soybeans. It is also used to saccharify rice, other grains, and potatoes in the making of alcoholic beverages such as huangjiu, sake, and shōchū. The domestication of A. oryzae occurred at least two thousand years ago." [2]

Has anyone got experience of koji fermentation?

[1] "TECHNIQUE FOR IMPROVED PRODUCTION OF 3,4 DIHYDROXY PHENYL L-ALANINE BY ASPERGILLUS ORYZAE"
SIKANDER ALI AND IKRAM-UL-HAQ
Pak. J. Bot., 39(2): 623-627, 2007.
http://www.pakbs.org/pjbot/PDFs/39(2)/PJB39(2)623.pdf

[2] http://en.wikipedia.org/wiki/Aspergillus_oryzae

John