(1) Alkaline phosphatases were
present in all subcellular fractions obtained by
ultracentrifugation of all the tissues examined.
(2) The highest specific activities (mU/mg protein) were found in the microsomal fractions,
the lowest in the supernatant, with the exception of the mammary tumour examined. (3) A
different thermostability of the enzymes in the
various fractions pointed to the presence of isoenzymes; a biphasic curve gave
evidence of the simultaneous presence of at least two isoenzymes in some particulate
structures. (4) There was no specific thermolabile pattern of alkaline phosphatases in
the malignant tissues examined, assuming the method used is valid for establishing
such differences.