Individual human infiltrating
ductal carcinomas and
fibroadenomas were sectioned frozen to yield an alternating sequence of stained and lyophilized material. Stained preparations were used as references permitting microdissection of regions of
tumor involvement in the corresponding dried sections. Tissues quantities of 5 to 25 micrograms dry weight were incubated under
mineral oil in reaction volumes of 5 microliters and analyzed for cyclic
adenosine 3':5'-monophosphate
phosphodiesterase (PDE). The observed affinity constants for the 27,000 x g soluble PDE from benign
tumors were 4.7 and 49.9 microM, while those for malignant
tumors were 6.3 and 28.5 microM. The soluble
enzyme of both
tumor types eluted in three peaks on
DEAE-Sephacel microcolumns. Both
tumor types possessed a PDE activator eluting at 350 mM NaCl, although endogenous PDE activities were unaffected by additions of either this activator or 200 microM
ethylene glycol bis(beta-aminoethyl
ether)N,N,N',N'-tetraacetic
acid. Individual microsections of benign
tumors contained total PDE levels 2-fold higher than those of malignant
tumors. Homogenates prepared from pooled microsections of the same
tumors possessed only one-half of the total activity. Differential losses of
enzyme in various preparation schemes as well as the use of
tumor samples differing in cell density were suggested to account for some of the apparently conflicting literature values for
breast tumor PDE.