Sorghum microsomes

Sorghum microsomal enzyme system Production of 25 from tyrosine, isomerization of oxime 25 to 26, and its conversion to hydroxymandelonitrile 106, 117... 

Sorghum microsomal enzyme system l-Nitro-2-(p-hydroxyphenyl)ethane is a precursor of oxime 25 = 0.05 mM and Vmax = 14 nmol mg h 106... 

The membrane-bound enzyme system In sorghum microsomes will catalyze the formation of HCN with N-hydroxytyroslne as substrate. The reaction requires O2 and NADPH. The apparent Km for N-hydroxytyroslne was 0.11 mM and a Vmav of 345 nmol HCN/hr/mg protein was observed. 

In microsomes from Sinapis alba L.,33,34 Tropaeolum majus L.,35,36 and Carica papaya L.,37 the aromatic amino acids (tyrosine and phenylalanine) have been shown to be converted to the corresponding oximes by cytochrome P450-dependent monooxygenases. The conversion of tyrosine to the corresponding oxime in microsomes from S. alba was approximately 1000 fold lower than in microsomes from the cyanogenic sorghum.33 This made a biochemical approach for the isolation... 

Moller, B.L. and Conn, E.E. (1980) The biosynthesis of cyanogenic glucosides in higher plants channeling of intermediates in dhurrin biosynthesis by a microsomal system from Sorghum bicolor.. Biol. Chem., 255, 3049-56. 

Table I presents data from McFarlane al, (8) showing that the multi-step oxidation of L-tyroslne to p-hydroxymandelonltrlle requires only 02 and a source of reducing power, most effectively supplied by an NADFH generating system. The table also shows that some of the L-tyroslne Is converted to p-hydroxyphenylacetaldoxime (aldoxime) as well as a trace of p-hydroxyphenylacetonltrlle (nitrile). The production of the aldoxime and nitrile In this experiment was the first Indication that the microsomal preparation from sorghum might constitute an organized enzyme entity Involved In the synthesis of dhurrln. If this were true, it should be possible to demonstrate each individual step of the reaction sequence between tyrosine and p-hydroxymandelontrlle.

Studies on the microsomal enzyme system in sorghum have been greatly facilitated by development of a method for separating the trlmethyl-sllyl (TMS) derivatives of the various intermediates on a gas-liquid... 

Many of the enzyme systems of the biosynthetic process have now been studied. A microsomal fraction from etiolated sorghum seedlings converted L-tyrosine (2) into p-hy-droxymandelonitrile (3) (Halkier and Mpller, 1991 Mpller and Poulton, 1993). The particles required only NADPH in addition to the substrate.. /V-Hydroxytyrosine (4) was shown to be an intermediate in the synthesis of the aldoxime, and an N-hydroxylating cytochrome P-450 was identified (Dewick, 1984 Halkier and M0ller, 1989,1991 Halkier et al, 1991). The A -hydroxytyrosine (4) is converted to 2-nitro-3-(p-hy-droxyphenyl)propionic acid (5), which is, in turn, converted to l-ad-nitro-2-(p-hydroxyphenyl)ethane (6). The last compound appears to be the immediate precursor to ( )-p-hy-... 

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