Further Observations on the in Vitro ⁶⁵Zn-binding Sites of Human Prostatic Tissues¹

In vitro ⁶⁵Zn-binding capacity of formalin-fixed tissue of human prostrate gland was reduced to less than 10% within 1 hour in HCl-methanol at 38°C. Treatment of the tissue sections with HCl-methanol for 16 hours abolished practically all the ⁶⁵Zn-binding capacities of prostatic tissues. However, the ⁶⁵Zn-binding capacity of HCl-methanol-treated sections was completely restored within 16 minutes in 0.2 n KOH in 90% ethanol. Thus, the in vitro ⁶⁵Zn binding of these tissues appears to be due to interaction with carboxyl groups and not with sulfates. When control (undesulfated) sections were reacted with KOH, there was an increase of 1.6-, 10-, and 40-fold in the ⁶⁵Zn-binding capacities in carcinoma, normal, and hyperplasia sections respectively. There was a comparable increase also with the desulfated sections. Apparently, sites capable of binding ⁶⁵Zn are unmasked by KOH; this unmasking, however, appears to follow a 16-minute lag phase of demethoxylation in normal tissue and in hyperplasia, but not in carcinoma. Moreover, the KOH-dependent ⁶⁵Zn-binding capacity appears to be directly related to the in vivo zinc concentration: high masked sites to high in vivo zinc concentration, in hyperplasia; low masked sites to low concentration, in carcinoma; and intermediate levels in normal prostate. Furthermore, curves based on ⁶⁵Zn binding after demethoxylation support the concept that hyperplasia is not a precursor to the development of neoplasia in the prostate gland.