The effects of a variety of albumin fractions and subfractions (human and bovine) on the steady state levels of the glycolytic intermediates and cofactors of muscle and adipose tissue were tested in vitro. In muscle, the pattern is characterized by decreases in pyruvate (Pyr), adenosinetriphosphate (ATP) and phosphocreatine (PC) and increases in phosphoenolpyruvate (PEP), 3 phosphoglycerate (3PG), αglycerophosphate (αGOP) and dihydroxacetonephosphate (DHAP). There are no marked changes in glycogen (Gly), glucose-6-phosphate (G6P), fructose-diphosphate (FDP), lactate (Lac), adenosine-mono- and diphosphates (AMP, ADP), and inorganic phosphate (Pi). The Lac to Pyr ratio is increased while the αGOP to DHAP ratio is unchanged. There appears to be no change in pyridine nucleotides in the presence of albumin.

Although all preparations tested were active in producing these substrate changes, the albumin molecule per se is probably not the active factor since albumin, from which a small molecular component designated as X is removed, has lost its capacity to alter the substrates of the glycolytic pathway as well as its insulin inhibitory activity.

The nature of the substrate changes in the presence of albumin suggests either a block of the pyruvate kinase enzyme with subsequent accumulation of glycolytic intermediates behind the block or an enhancement of conversion of Pyr to PEP. Studies with Pyr indicate the capacity of muscle to convert Pyr to PEP, but they do not elucidate the nature of the albumin-induced substrate changes.The addition of insulin or anti-insulin serum in vitro does not reverse these changes.

In rat adipose tissue the presence of albumin does not inhibit insulin action nor does it appear to produce the above substrate changes.

The pathophysiologic significance of these observations remains to be demonstrated.

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