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Biomedical subjects

H A KREBS

Publications and source records attributed to H A KREBS.

At least 19 recordsLinked to original sources
PubMed1965

FRUCTOSE 1, 6-DIPHOSPHATASE IN STRIATED MUSCLE.

1. 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. 2. 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 mumoles of substrate were split/g. fresh wt./hr. at 22 degrees . 3. Like liver fructose diphosphatase, the muscle enzyme is inhibited by substrate concentrations above 0.1 mm, by AMP and by trace quantities of Zn(2+), Fe(2+) and Fe(3+); it is ;activated' by EDTA. Inhibitions by the above agents may account for the failure of previous authors to detect the enzyme. 4. Heart muscle of several vertebrate species and the smooth muscle of pigeon and fowl gizzard had no measurable activity. 5. The presence of fructose diphosphatase and the virtual absence of the enzyme systems converting pyruvate into phosphopyruvate means that lactate and pyruvate cannot be converted into glycogen in muscle, whereas the phosphorylated C(3) compounds can. The reconversion into carbohydrate of lactate (which readily diffuses out of muscle) occurs in liver and kidney only. The reconversion of phosphorylated C(3) intermediates (which cannot diffuse out of the tissue) can occur only within the muscle. 6. 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.

Adenine↗
PubMed1965

ACCELERATION OF RENAL GLUCONEOGENESIS BY KETONE BODIES AND FATTY ACIDS.

1. Acetoacetate or short-chain fatty acids (acetate, butyrate, propionate, n-hexanoate, n-octanoate) accelerate the rate of glucose formation from lactate, fumarate and other precursors in slices of kidney cortex (rat, rabbit, sheep). The cause of this acceleration has been investigated. 2. There are two different mechanisms of acceleration. At low concentrations of glucogenic precursors the acceleration is mainly due to a ;sparing' action. The substances which accelerate are oxidizable and serve as fuel of respiration in place of the glucogenic precursor. This is indicated by the fact that the ratio lactate used/glucose formed falls in the presence of the accelerators and approaches the value 2. 3. At high concentrations of lactate the acceleration appears to be mainly due to the activation of pyruvate carboxylase by acetyl-coenzyme A. The evidence in support of this is summarized. The results indicate that the activation of pyruvate carboxylase by acyl-coenzyme A discovered by Utter & Keech (1963) in purified enzyme preparations also occurs in crude tissue homogenates and can play a part in the control of oxaloacetate synthesis and gluconeogenesis.

Acetates↗