Peter W Hochachka

1. The properties of fructose diphosphatase from the liver of rainbow trout (Salmo gairdnerii) were examined over the physiological temperature range of the organism. 2. Saturation curves for substrate (fructose 1,6-diphosphate) and a cofactor (Mg(2+)) are sigmoidal, and Hill plots of the results suggest a minimum of two interacting fructose 1,6-diphosphate sites and two interacting Mg(2+) sites per molecule of enzyme. 3. Mn(2+)-saturation curves are hyperbolic, and the K(a) for Mn(2+), ...

We develop a unifying theory of hypoxia tolerance based on information from two cell level models (brain cortical cells and isolated hepatocytes) from the highly anoxia tolerant aquatic turtle and from other more hypoxia sensitive systems. We propose that the response of hypoxia tolerant systems to oxygen lack occurs in two phases (defense and rescue). The first lines of defense against hypoxia include a balanced suppression of ATP-demand and ATP-supply pathways; this regulation ...

During the last half century or more, studies of diving physiology and biochemistry made great progress in mechanistically explaining the basic diving response of aquatic mammals and birds. Key components of the diving response (apnea, bradycardia, peripheral vasoconstriction, redistribution of cardiac output) were found in essentially all species analyzed and were generally taken to be biological adaptations. By the mid 1970s, this approach to unravelling the diving response had run ...

Alanopine dehydrogenase (alanopine: NAD oxidoreductase) was purified from the adductor muscle of the Japanese oyster, Crassostrea gigas Thunberg. This enzyme catalyzes the reductive imination between pyruvate and alanine, or glycine, utilizing NADH as coenzyme, producing 2,2′-iminodipropionic acid (alanopine), or 2-methyliminodiacetic acid (strombine). The enzyme can be readily purified to a specific activity of 700 units/mg protein. The molecular weight was 47000 ± 4000 when measured by ...

The term homeostasis traditionally refers to the maintenance of a relatively constant internal milieu in the face of changing environmental conditions or changing physiological function. Tissues such as skeletal and cardiac muscles must sustain very large-scale changes in ATP turnover rate during equally large changes in work. In many skeletal muscles, these changes can exceed 100-fold. In unique biological circumstances (for example, during periods of oxygen limitation, vasoconstriction ...

We investigated structural characteristics for high O2 flux in hummingbird flight muscle, i.e. the most O2 demanding skeletal muscle per unit tissue mass among vertebrates. Pectoralis and supracoracoideus muscles of 3-4 g hummingbirds (Selaphorus rufus) were perfusion fixed in situ, processed for electron microscopy and analyzed by morphometry. Small fiber size (group mean +/- SE, 201 +/- 14 microns 2 at 2.1 microns sarcomere length), large capillary length per fiber volume (8947 +/- 869 ...

The present study was conducted to investigate the potential role of changes in the apparent K(m) for ADP and in the functional coupling of the creatine (Cr) kinase (CK) system (CK efficiency) in explaining the tighter integration of ATP supply and demand after exercise training. Mitochondrial function was assessed in saponin-skinned fibers from the soleus and the deep red portion of the medial gastrocnemius isolated from trained (T; treadmill running, 5 days/wk, 4 wk) and control (C) ...

In heart and red muscle of dogfish (Squalus acanthias), the maximal activities of the fatty acid catabolizing enzyme carnitine palmitoyltransferase (CPT) are less than 5% the rate in the same tissues of teleosts (carp, Cyprinus carpio; trout, Salmo gairdneri). CPT activities in these tissues of hagfish (Eptatretus stouti) are approximately 10% the rate in teleosts. However, the maximal activities of the beta-oxidation enzyme beta-hydroxyacyl-CoA dehydrogenase (HOAD) in dogfish red muscle ...

Organisms vary widely in their tolerance to conditions of limiting oxygen supply to their cells and tissues. A unifying framework of hypoxia tolerance is now available that is based on information from cell-level models from highly anoxia-tolerant species, such as the aquatic turtle, and from other more hypoxia-sensitive systems. The response of hypoxia-tolerant systems to oxygen lack occurs in two (defense and rescue) phases. The first lines of defense against hypoxia include a drastic, ...

Phosphofructokinase (EC 2.7.1.11) occurs in turtle heart at a specific activity of about 19 units per g wet weight; Mg2+ or Mn2+ can satisfy the divalent cation requirement; ATP, GTP, or ITP all can serve as phosphate donors for the reaction. Although the pH optimum for the enzyme is pH 7.5, the intracellular pH of the anoxic turtle heart, pH 6.8, was chosen for characterizing the enzyme. At this pH, turtle heart phosphofructokinase displays hyperbolic saturation kinetics with respect to ...

Citrate synthase occurs in two kinetically distinguishable forms, termed C and W in cold and warm acclimated trout, respectively. Oxalacetate and acetyl-CoA saturation curves for both enzymes are hyperbolic and do not show any substrate inhibition. The apparent Km values for the C form increase with temperature above 10°. At saturating (0.1 mm) levels of oxalacetate, the Km of acetyl-CoA is 0.05 mm at 10°, about one-fifth the value at 35°. At saturating levels of acetyl-CoA, the Km of ...

1. The activity of glutamate dehydrogenase was measured in the tissues of the squid, Loligo pealeii. The enzyme occurs in high activity in digestive pouch, systemic heart, and all muscle tissues. 2. Glutamate dehydrogenase from mantle muscle is located intra-mitochondrially, has a molecular weight of 310,000, and is electrophoretically similar to the enzyme from all other squid tissues. 3. The enzyme from mantle muscle was purified 40-fold by elution from DEAE-cellulose and used for ...