Three 0,-dependent reactions are involved in the removal of C-19 as formate, in oestrogen biosynthesis; it is shown that the oxygen atoms introduced in steps 1 and 3 of the process are the ones which are found in the biosynthetic formate.

No abstract

It is shown that both vinyl groups of haem are formed through the loss of S hydrogen atoms located a t /?-positions of the propionic acid side chains; the hydrogen atoms at the a-positions of the side chains are not involved in the biosynthesis of haem. /?-hydrogen is retained. A mechanism of the latter type is suggested by the work of S a n ~. ~The presence of vinyl groups as well as intact propionic acid side chains within the same molecule ( 5 ) may serve as reliable indicators for giving information on the reaction, -CH,-CH,-CO,H -+ -CH = CH,, in isotopic studies.When 5-amino-[3,5-3H4]laevulinic acid [ (2a), 5 mg, 13 x 106c.p.m./mg], containing 43% of the total radio-CONTINUING studies on the mechanisms of enzymic activity a t C-5 and the remainder a t C-3, was incubated for reactions involved in porphyrin biosynthesis,lS2 we now 8 h at 37' with a haemolysed preparation4 of anaemic? chick

Dinitro benzoate, etc. 5965 * For the preparation of tritiated cholecalciferol for biological purposes, we recommend its isolation from the equilibrium mixture by thin-layer chromatography rather than via the 3,5-dinitrobenzoate.These reactions have been reviewed by ( a ) M.

The second sentence of the Scheme 3 caption should read: The decomposition of the adduct 6 may occur by a concerted process (---+) or a stepwise radical mechanism as shown.The correct Scheme 4 is given below.