Nature of inhibition of rat testicular alkaline phosphatase by isatin

Summary Isatin has been found to inhibit rat testicular alkaline phosphatase (EC 3.1.3.1). That the inhibition is non-competitive as well as non-allosteric is evident from a) the hyperbolic curve relating inhibition as a function of inhibitor concentration; b) the small change in enthalpy, free energy and entropy; c) the number of isatin molecules associating with 1 molecule of the enzyme (n=1.29); and, d) the decrease in the values of both K_m and V_max in the presence of isatin.     

Thyroid activity in response to some gonadal steroids in methallibure-treated Heteropneustes fossilis (Bloch).

Methallibure treatment is as effective as hypophysectomy in reducing thyroid activity in H. fossilis. Sex steroids (TP and EB) administration restored thyroid activity in methallibure-treated females to normal level, but failed to elicit any response in males. This drug seems to block TSH secretion and thyroid hormone synthesis in H. fossilis.     

Contraction of frog stomach muscle and heart in non-ionic solutions

Zusammenfassung Herz und Magenmuskulatur des Frosches verlieren in halb-isotoner Rohrzuckerlösung innert 1 h alles Natrium. Trotzdem bleibt die spontane Kontraktilität erhalten. Natrium ist also für die Erregbarkeit dieser Muskeln nicht Voraussetzung.