Spinach carbonic anhydrase subjected to gel chromatography revealed two active fractions. One corresponds to the previously identified hexameric form of the enzyme while the second transient fraction has a molecular weight corresponding to a dimeric form. The dehydrase activity of the enzyme with respect to HC03-was investigated using a stopped-flow technique. Values of the Michaelis-Menten kinetic parameters K , and k,,, (=k2) were determined as a function of pH between 6.2 and 7.6 in phosphate and Nmethylimidazole buffers. Values of K , remained essentially constant around 34 mM in N-methylimidazole buffers, but increased significantly in phosphate buffers as the pH decreased. The behavior of the turnover number k,,, with respect to pH was found to be consistent with a titratable activity linked group having an apparent pK, of 7.7 as was shown earlier for C 0 2 hydration catalyzed by this enzyme (Pocker,
Bestimmung der Verschlackbarkeit bei 1550 und 1650°mit zahlreichen Oxyden. Geringer Angriff polyniirer Schlacken, Schlackenangrijf geht von den FlufJmitteln des Tiegels aus. Erkliirung der geringen Verschlackbarkeit von M agnesit und maqnesiareichem Schmelzen durch amphotere Eigensch'tften der Magnesia.)
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