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1. (1) A procedure for isolating pure ubiquinone-50 form horse heart is described. 2. (2) A method of determining the ubiquinone content of heart and heart-muscle preparation is give. 3. (3) Treatment of ubiquinone with ascorbic in HCl in the presence of pyrogallol gives a reduction product,in about 30% yield, whihc is not the smae as ubiquinol. Its properties suggest that is is ubichromanoll or derivative thereof. 4. (4) This product is not distinguishable from α-tocopherol by the procedure previously used for measuring the α-tocopherol content of heart-muscle preparationa nd is responsible for the “extra α-tocopherol” previoulsly reported therein. 5. (5) Vitamin K 1 treated under similar conditions also gives a stable reduction product which is also probably a chromanol. 6. (6) Our previous reporat that the Keilin and Hartree heart-muscle preparation contained α-tocopherol has been confiremd. The tocopherol was identified by chromatography on ZnCO 3 -impregnated paper and on alumina ( 14 C-labelled α-tocopherol acting as a marker), by its u.v.-absorption spectrum and by the absorption spectrum characteristic of α-tocopherylquinone obtained by oxidation with AuCl 3 . 7. (7) The Keilin and Hartree heart-muscle preparatino from horse containes on the average 0.4 μmole α-tocopherol/g protein (9 preparations) and 9.1 μmoles ubiquinone/g protein (9 preparations). For ox, the values are 0.8 (3 preparations) adn 2.9 (one determination) respectively. Little if any α-tocopherylquinone (less than μmole/g protein) was found in the ox preparation. 8. (8) Virtually all the α-tocopherol and ubiquinone found in the heart is located in the sarcosomes (mitochondria). 9. (9) α-Tocopherol is not a precursor in the biosyngthesis of ubiquinone in rabbit heart or liver. 10. (10) α-Tocopherol, α-tocopherylquinol adn ubiquinol inhibit the ATP-P 1 exchange reaction fo rat-liver mitochondria and stimulate the ATPase.

A method for the determination of insulin potency using circular chromatography is described. The eluted spots are measured with respect to a standard which is run simultaneously with the unknown. The results of this determination do not differ significantly from those obtained by biological assay, at least for preparations with a potency higher than 19 I.U./mg on a moisture-free basis. For the determination of less pure samples the use of a standard insulin of corresponding purity is recommended. The precision of the method compares with that of a biological assay with 250 rabbits. Protamine and excess of zinc do not interfere with the determination.