I955 more acidic solutions, with pH < 7 0, a few seconds elapsed before equilibrium was attained. Taking into account the ionization of the haem-linked group on MetMb and the higher oxidation state, the variation of Kb,. with pH is shown to confirm the conclusion that 2 moles of H+ are liberated/mole of acidic MetMb. Using 6-1 for the pK of the group in MetMb as established in other studies, the results give a pK of 75 for the group in the higher oxidation state at 200 and I = 0 04. 3. The variation of KRb, with temperature gives AHO = 10-0 ± 2*0 kcal./g.mol.: if the ionization of the haem-linked group is allowed for, the value 9*0 ± 1.0 kcal./g.mol. is obtained. 4. The dependence of Kob. on ionic strength is in accord with a change in charge from + 1 on MetMb to zero on the higher oxidation state. 5. The results are shown to favour the ferryl ion structure, or an isomer of this structure, for the higher oxidation state. The isomeric structures would, in general, require the presence of another ionizing group in myoglobin, but no evidence for such an ionization could be found. With other direct evidence favouring the ferryl ion structure this is to be preferred, and the higher oxidation state may provisionally be named ferrylmyoglobin. We gratefully acknowledge grants from the Department of Scientific and Industrial Research, and the Medical Research Council, held by one of us (D.H.I.) during the course of this investigation.

PARTICULATE ACID PHOSPHATASE 433 2. The partial activation which occurs in hypotonic media takes place very rapidly, does not show a further increase if the time of exposure at 0°is prolonged and is not reversed by a return to isotonicity. 3. Inorganic univalent salts afford only transient osmotic protection. In contrast, part of the sucrose can be replaced in the medium by an iso-osmolar quantity of ,B-glycerophosphate, with no adverse effect on the stability of the granules. 2:4-Dinitrophenol is without significant influence on the activation of acid phosphatase. 4. The activation which occurs when the granules are incubated at 370 in 0-25m sucrose is much more rapid at pH 5 than at pH 6-1. 5. The internal enzyme appears to be entirely inaccessible to external glycerophosphate at pH 5, but seems to contribute significantly to the free activity of intact preparations as the pH is raised, or as the temperature is increased at pH 6-1. 6. The results obtained afford additional support for the sac-like representation of the acid phosphatase-containing granules arrived at in earlier work. It is pointed out that a limited degree of permeability of the membrane to glycerophosphate remains compatible with perfect osmotic protection by this compound, as long as its rate of inward diffusion does not exceed the rate at which it can be hydrolysed within the granules and eliminated in the form of glycerol and inorganic phosphate. These investigations have been supported by grants from the 'Centre National de Recherches sur la Croissance normale et pathologique', the Rockefeller Foundation and the Lilly Research Laboratories.

No abstract

One of the sulphatases of rat liver, like acid phosphatase, is enclosed within cytoplasmic granules. The two enzymes are released from these granules in similar proportions by various treatments.