Individual muscle fibers of 10 motor units from the tibialis posterior muscle of cat were identified by glycogen depletion techniques, characterized for histochemical type, diameter, and intramuscular locations, and analyzed by quantitative biochemical methods. Four enzymes, representing different energy-yielding pathways, were quantitatively assayed in muscle fibers belonging to motor units selected from each of the three major physiological types. All four enzymes demonstrated identical activities among fibers within a motor unit, while showing up to 11-fold differences among fibers belonging to different motor units. Moreover, fibers within a single motor unit, but of substantially different diameters, were nevertheless homogeneous in specific enzyme activities.

Individual fibers of prospective fast (extensor digitorum longus; EDL) and slow (soleus) muscles of rats have been analyzed to determine the profiles of key energy-generating enzymes at successive stages of postnatal development. Mean activities of lactate dehydrogenase (LDH) and adenylokinase (AK), 2 enzymes associated with contractile function, are significantly different in the 2 fiber populations at birth; furthermore, wide variations in enzyme activities exist among the individual fibers. There is a progressive refinement of enzyme levels in the soleus into a more uniform fiber population, while the fibers in the EDL progressively diverge into 2 distinct phenotypes. Changes in EDL and soleus are punctuated by periods of rapid change, with the period between 10 and 21 d being most eventful. Generally, the maturation profiles of LDH and AK coincide with the transition from neonatal to adult fast myosins and closely reflect the timing of energy demands imposed by contractile activity patterns. In contrast, activities of the oxidative enzymes malate dehydrogenase and beta-hydroxyacyl CoA dehydrogenase are similar in both muscles at birth and steadily increase during the first 3 weeks, suggesting a progressive adaptation to the aerobic extrauterine environment. After 30 d, there are differential changes in the oxidative profiles of enzymes for fatty acid and glucose metabolism. The profiles follow dietary changes associated with weaning, which suggests a phenotypic dependence of neonatal muscle on the particular available energy substrate. All enzymes are low in all fibers of EDL and soleus at birth, indicating their modest metabolic capacity.(ABSTRACT TRUNCATED AT 250 WORDS)

Motor units from the cat tibialis posterior muscle were examined for an association between physiological and biochemical properties. Functionally isolated motor units were categorized on the basis of their physiological properties. This was followed by quantitative microbiochemical analysis of single muscle fibers from each unit, identified in cross sections using the glycogen-depletion method. The activities of malate dehydrogenase and beta-hydroxyacyl-CoA dehydrogenase distinguished between fatigable (type FF) and fatigue-resistant (types FR and S) units. The activities of both lactate dehydrogenase and adenylokinase were higher in fast- than in slow-contracting units. Cluster analyses, based on both physiological and biochemical properties or on biochemical properties alone, produced groupings identical to types FF, FR, and S. The association between physiological and biochemical properties substantiates the idea that biochemically distinct groups of motor units correspond to physiologically identifiable groups.

A B S T R A C T We isolated and partially characterized three Fe-binding macromolecules from human leukocytes. Mononuclear cells from normal individuals and from five patients with chronic lymphocytic leukemia and neutrophils from normal donors were surface radiolabeled by using 125I and lactoperoxidase.After detergent solubilization of the cells, Fc,-binding macromolecules were purified by repetitive affinity chromatography under a variety of conditions and analyzed by sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis.Three radiolabeled macromolecules were isolated that retained specific ability to bind to Fc fragments.A 52,000-64,000-mol wt macromolecule was isolated from normal mononuclear and polymorphonuclear cells. A 43,000-mol wt band was characteristic of mononuclear cells, particularly from patients with chronic lymphocytic leukemia. A 33,000-mol wt molecule could be obtained from normal leukocytes under conditions that suggest it might be a proteolytic fragment.

The activities of lactate dehydrogenase, malate dehydrogenase, phosphorylase, and adenylate kinase were measured in single myotubes dissected from primary cultures of rat skeletal muscle. For a given enzyme, activities among the spontaneously contracting cells varied as much as eightfold. When the myotubes were paralyzed with tetrodotoxin, the variability in enzyme levels was markedly decreased. These and other findings suggest that differences in enzyme levels among individual myotubes may arise as a result of differences in their pattern of contractile activity.