Relationships of quantitative structure-activity for normal aliphatic alcohols.

The relative toxicity of 14 normal aliphatic alcohols has been determined as 48-hr 50% population growth inhibition (log BR, biological response) of Tetrahymena pyriformis. A linear relationship was observed between log BR and the 1-octanol/water partition coefficient (log Kow). Comparison of log BR with 96-hr 50% mortality data for Pimephales promelas revealed excellent agreement between the two test systems. A relatively constant steady-state biophase toxicant concentration is calculated for each alcohol. Calculated chemical activity increased with an increase in hydrocarbon chain length. In addition, there was good agreement between chemical activity and the activity coefficient for narcosis.

Studies on the transverse tubule membrane Mg-ATPase. Lectin-induced alterations of kinetic behavior.

Transverse tubule (TT) membrane vesicles contain a very active Mg-ATPase (EC 3.6.1.3). Concanavalin A (ConA) and other lectins were found to activate the TT Mg-ATPase from chicken skeletal muscle up to 25-fold yielding specific activities greater than 800 mumol/h/mg. The sarcoplasmic reticulum Ca-ATPase and the sarcolemma Na,K-ATPase were unaffected by ConA. 125I-Labeled lectin binding to the TT membrane Mr 102,000 glycoprotein supports the contention that this protein is identical with or is intimately associated with the TT Mg-ATPase. The ATPase exhibited non-Michaelis-Menton kinetics with both apparent negative cooperativity (n = 0.723; S0.5, Mg-ATP = 14 microM) and substrate inhibition (Ki, Mg-ATP = 10.2 mM), both of which were eliminated in the presence of ConA. Under the same conditions, ConA also abolished the unusual temperature dependence and potent Triton X-100 inhibition. The similarities in ConA suppression of both Triton and substrate inhibition suggest that these ligands may be interacting through a non-catalytic site and that Triton is serving as a nucleotide-mimetic agent. The unique kinetic responses are consistent with a homotropic substrate modifier mechanism wherein the enzyme can be viewed as possessing a single catalytic and a single regulatory site on a single polypeptide chain. It is proposed that ConA interferes either with ligand interaction at a putative regulatory site or blocks communication between a regulatory site and the catalytic site. The possible nature of the regulatory site and its modulation by a ConA-like, endogenous, skeletal muscle lectin and their combined role in excitation-contraction coupling is discussed.

Characterization of transverse tubule membrane proteins: tentative identification of the Mg-ATPase.

Vesiculated fragments of chicken skeletal muscle transverse tubule (TT) membranes were analyzed for their content of loosely associated and integral membrane proteins. Of particular interest was the identification of the magnesium-stimulated ATPase (Mg-ATPase), which is characteristically located in native isolated TT vesicles of chicken skeletal muscle [R. A. Sabbadini and V. R. Okamoto (1983) Arch. Biochem. Biophys. 223, 107-119]. A number of the proteins found in vesicular TT preparations were found to be extractable by a mild Triton-X100 treatment and were identified as aldolase, enolase, creatine kinase, glyceraldehyde-3-phosphate dehydrogenase, lactate dehydrogenase, and pyruvate kinase. Approximately 60% of TT-associated protein was extracted with Triton, resulting in a twofold enrichment of the Mg-ATPase. Concommitantly, one core integral membrane protein possessing a Mr of 102,000 was enriched, suggesting that it is responsible for the Mg-ATPase activity present in chicken skeletal muscle TT membranes.