Abstract
The finding in frog and rabbit sciatic nerves of a soluble phosphorus compound behaving like the phosphocreatine of muscle 1 suggested the desirability of a similar study of nerve creatine.
Total creatine was determined, after digestion of the whole tissue for 3 hours in N H2SO4 on a water bath, by the usual picric acid method. For estimating “free” and “bound” creatine, the cold tissue was extracted with iced trichloracetic, alcohol added to an aliquot portion to a concentration of 66% and the bound creatine precipitated with crystalline Ba(OH)2 (Eggleston, 2 for separating phosphocreatine). The 2 fractions were then heated with acid and determined as above. Controls showed full recovery of creatine in the “free” fraction and phosphocreatine (kindly supplied by Dr. Fiske) largely in the “bound” fraction.
The total creatine content of green frog sciatics varies markedly with the season or condition of the animals, although values for nerves from one frog agree within 6%. From June 4th to July 27th the values rose entirely regularly in 11 successive experiments a few days apart, from 104 mgm. % to 234 mgm. %. The muscles showed a similar but less regular rise from 440 mgm. % to 570 mgm. % (average 500 mgm. % for 13 experiments). The average total creatine in the nerves, in 30 experiments extending from May to January, was 164 mgm. %. A similar average for the bull frog sciatic, based on 20 experiments, was 135 mgm. %, but in this series fewer of the analyses were made during the periods of high concentration than in the case of the green frogs. Two determinations of total creatine in dog's sciatic yielded 139 and 140 mgm. %.
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