DISTURBANCES IN THE GLYCOLYTIC FERMENT SYSTEM OF SKELETAL MUSCLE

Abstract

1. In intact rabbit's muscle undergoing rigor mortis changes, all the phosphoric acid in labile combinations, and also some more firmly bound as hexose monophosphate, are set free. When the muscle after death is minced, phosphoric acid is again set free, but it is in part used for esterification, and hexose esters appear which form insoluble calcium salts (diesters). These esters, if present at all in fresh muscle or intact rigor mortis muscle, are only in extremely small amount. In monoiodoacetate poisoned muscle the free orthophosphate, and also that obtained from compounds with labile phosphoryl linkages, are rapidly esterified. Just before rigor sets in, the free orthophosphate is diminished to a greater extent than in any other type of muscle examined. Both forms of ester accumulate, the mono‐ and the di‐ester, the latter remaining at a fairly steady level (20 per cent.). In this muscle, unlike the others, extremely little lactic acid is produced during the rigor.2. Ferment extracts of rigor mortis muscle produce predominant esterification with small lactic acid production, but addition of adenosine triphosphate restores the normal glycolytic power. Similar extracts of monoiodoacetate muscle produce esterification practically alone, and addition of the above nucleotide increases the esterification without restoring glycolysis.3. Inactivated extracts of fresh muscle are readily reactivated by the addition of the natural nucleotide, and, associated with the esterification, there is the normal lactic acid production. Inactivated extracts obtained by prolonged dialysis require the addition of the magnesium ion. The co‐ferment activity of the boiled extract of fresh muscle is proportional to the amount of adenosine triphosphate extracted.4. The co‐ferment activity of the nucleotide derivatives is in the following order:— Adenosine triphosphate (or boiled muscle extract) 〉 adenylic acid 〉 inosine triphosphate 〉 inosinic acid 〉 adenine + ribose phosphate.5. At low temperatures, almost immediately after mixing slightly active ferment extracts and substrate with adenosine or inosine triphosphate, the loosely bound H3PO4 of the nucleotide passes into a new organic combination with a firmer linkage. At this time the orthophosphate value is unaltered, but later this falls, and with the esterification lactic acid production commences.6. When adenylic acid is added to ferment extracts in incubation mixtures it rapidly combines with orthophosphate to form adenosine triphosphate, and then follow the processes of esterification and glycolysis.Rabbit's skeletal muscle was used for all experiments, and the methods employed for analysis were briefly as follows:— 1. Deproteinisation and acid extraction. One part minced muscle mixed with coarse quartz sand, extracted with approximately 3 parts 5 per cent. trichloroacetic acid, filtered and neutralised. 2. Phosphorus estimations by slightly modified FISKE and SUBBAROW's method. 3. Lactic acid by FRIEDEMANN, COTONIO, and SHAFFER method. 4. Nucleotide preparations. The adenosine triphosphate by FISKE and SUBBAROW'S method. The other derivatives as described in text.