In a survey of normal and cancerous human tissues we determined the distribution of immunoreactive prostatic acid phosphatase, using rabbit antiserum to acid phosphatase purified from prostatic fluid. In all normal tissues and blood cells studied except leukocytes we found less than 0.1% (expressed as micrograms per gram of wet weight of tissue) of the quantity of immunoreactive prostatic acid phosphatase detected in normal prostate tissue by radioimmunoassay. A small quantity of cross-reactive antigen (2.5 microgram/10(8) cells) was found in leukocytes. In all normal and cancerous nonprostate tissues surveyed by an immunohistochemical technique we detected no immunoreactive prostatic acid phosphatase, except in kidney tissue. Faint but reproducible staining was detected in the lumen of distal tubules and collecting ducts and within interstitial capillaries. Immunoreactive prostatic acid phosphatase was detected in the urine of pre- and post-pubertal males and females. We propose that this material is from serum (low concentrations of immunoreactive prostatic acid phosphatase are present in the serum of men and women) and that it is excreted into urine by the kidneys. Full proof of this must await future experimentation. The specificity of our antiserum for prostatic acid phosphatase was demonstrated by the fact that the Mr 100 000 and 20 000 liver acid phosphatase isoenzymes did not cross with our antiserum in either the radioimmunoassay or double-diffusion analysis. Similarly, preparations of isoenzymes 5A and 5B are human serum albumin did not cross react.

We wished to identify a 44-kD peptide isolated from lens membrane fractions which has apparent immunoreactivity to antivimentin and to antiphakinin. Urea-soluble proteins from rat lens membrane fractions were separated by two-dimensional electrophoresis, transferred to polyvinylidene fluoride membranes and probed with monoclonal antibodies to vimentin or cytokeratins, or a polyclonal antibody to phakinin. The monoclonal antibody to vimentin recognized the expected protein (M_r = 56 kD, pI = 5.1) and several smaller and more acidic peptides including a 44-kD spot with a pI of 4.9. A similar pattern of immunoreactivity was found with commercially available purified vimentin. The polyclonal antibody to phakinin recognized the expected protein (M_r = 52 kD, pI = 5.0) and several smaller and more acidic peptides, including a 44-kD spot with a pI of 4.9. Matrix-assisted laser desorption ionization mass spectroscopy analysis of the tryptic digest of the spot corresponding to 44 kD and pI of 4.9 identified neither vimentin nor phakinin but did identify peptides derived from ovalbumin (added to samples as an internal standard) and cytokeratin 1. Antibodies which recognize cytokeratin 1 reacted weakly with a 44-kD peptide which comigrated with the 44-kD vimentin-immunoreactive peptide in adjacent lanes of single-dimension SDS polyacrylamide gels. The 44-kD acidic (pI = 4.9) peptide which reacts with a monoclonal antibody to vimentin may be derived from cytokeratin 1.