FRUCTOSE 1, 6-DIPHOSPHATASE IN STRIATED MUSCLE

Abstract

The occurrence of fructose diphosphatase in muscle tissue was investigated with reference to the question whether lactate can be converted into glycogen in muscle, as postulated by Meyerhof (1930), fructose diphosphatase being one of the enzymes required for this conversion. Fructose diphosphatase was found in skeletal muscle of man, dog, cat, rat, mouse, rabbit, guinea pig, cattle, sheep, pigeon, fowl and frog. Under the test conditions between 5 and 60 [mu]moles of substrate were split/g. fresh wt./hr. at 22[degree]. Like liver fructose diphosphatase, the muscle enzyme is inhibited by substrate concentrations above 0.1 m[image]. by adenosine monophosphate (AMP) and by trace quantities of Zn2+, Fe2+ and Fe3+ it is "activated" by ethylenediamine tetraacetate (EDTA). Inhibitions by the above agents may account for the failure of previous authors to detect the enzyme. Heart muscle of several vertebrate species and the smooth muscle of pigeon and fowl gizzard had no measurable activity. The presence of fructose diphosphatase and the virtual absence of the enzyme systems converting pyruvate into phosphorpyruvate means that lactate and py-ruvate cannot be converted into glycogen in muscle, whereas the phos-phorylated C3 compounds can. The reconversion into carbohydrate of lactate (which readily diffuses out of muscle) occurs in liver and kidney only. The reconversion of phosphorylated C3 intermediates (which cannot difffuse out of the tissue) can occur only within the muscle, [alpha] -Glycerophosphate is probably the main intermediate requiring conversion into glycogen, The possible role of [alpha] -glycerophosphate formation in vertebrate muscle, already well established in insect muscle, is discussed.