Stability of Prostatlc. Acid. Phosphatase. In Normai Human. Sera. To the Editor: Not only are radioimmunoassays for prostatic acid phosphatase (EC 3.1.3.2).
not equally sensitive
for all sugars, and it can not be used with ion-exchange Chromatoplates. We believe that this reagent, or others based on a similar principle, can find their application in other branches of thin-layer chromatography. A. B. Benko L. D. Szabo “Frederic Joliot-Curie” Nat. Res. Instit. for Radiobiology and Radiohygiene H-i 775 Budapest, Hungary
Table 1. Stability of Acid Phosphatase as Assessed lmmunoassays and by Enzyme Assay ClinIcal
Yang Labs
Assays
IncubatIon
4.6
11.8
10.3
7days,4#{176}C
4.4 10.8
7.1 9.2
6.2 10.1
4.5 9.8
6 h, 23 #{176}C
3.8 9.2
4.9 9.8
6.0 10.7
4.0 7.5
24 h, 23 #{176}C
2.3
3.0
4.8
1.0
6.7
7.7
10.2
4.3
0.7 1.1
0.7 1.4
acid phosphatase
to temperature
at the
pH of serum
it is important that the time the samples are kept at tempera-
tures above 4 #{176}C be minimized.
The
discrepancy between the stabilityof
prostatic acid phosphatase observed and that previously described may be due to the method of purification of Foti et al. (1), which appears to yield a partly purified preparation (5). 3
4
S
8
‘
24
HO8
Fig.1. Loss of Immunological activity (chvles) andenzymlcactivity (squares) of prostatic acid ghosPhatase as a function of time at 37 C (open symbols) and 23 #{176}C (filled symbols)
4.5
10.4
nological activity was lost much faster than that described earlier. For example, To the Editor: we observed the assay value was half as Not only are radioimmunoassays for large after 1.5 h at 37 #{176}C, but Foti et al. prostatic acid phosphatase (EC 3.1.3.2) (3) detected no loss under these condimore sensitive and specific than earlier tions. enzymic methods (1, 2) but the immuWe then compared the sensitivity of nological activity of the enzyme is more several commercial radioimmunoassays stable than the enzymic activity of the to the inactivation of prostatic acid enzyme. We have examined the lability phosphatase in serum. Table 1 shows of the enzymic and immunological acthe results of assaying serum standards tivities of the protein and compared after various incubation conditions by them with earlier data (Figure 1 of ref. use of radioimmunoassay kits commer3). We find the immunological activity cially available from New England Nuof the protein to be far more labile than clear, North Billerica, MA 01862; Yang that report would indicate, and careful Laboratory, Bellevue, WA 98005; and handling of the patient’s sample is ClinicalAssays, in addition to data on therefore required to avoid obtaining the enzyme activity. Purified prostatic falsely low values for prostatic acid acid phosphatase was added to sera from phosphatase. normal men to give values of about Sand Figure 1 shows the progressive loss of 10 pg/L. Enzyme activity was measured both immunological and enzymic acagainst standards of purified prostatic tivity of the enzyme at 23 and 37 #{176}C.acid phosphatase. With all radioimmuPurifiedprostatic acid phosphatase (4) noassays, 2 hat 37#{176}C sufficed to destroy was added to normal male sera to give a most of the immunological activity. In final concentration of about 25 pg/L. each case the percentage loss of enzyme The radioimmunoasaay used was the kit activity exceeded the loss of immunoof Clinical Assays, Cambridge, MA logical activity. The latter was highly 02139; the enzyme method was that of sensitive to temperature; it was preWorthington Diagnostics, Freehold, NJ served for seven days at 4 #{176}C but was 07728. At both temperatures, immunolost after 2 hat 37 #{176}C; at 23 #{176}C, activity logical activity deteriorated more slowly was preserved for several hours. than enzymic activity, but the immuIn view of the sensitivity of prostatic
2
5.7
11.3
Stability of Prostatlc Acid Phosphatase In Normai Human Sera
1
Enzym. assay
HEN
Enzym., pgIL
4.7
None
2 h,37 #{176}C
0
by Various Radio-
References 1. Foti, A. G., Cooper, J. F., Herschman, H., and Sapon, S. R., The detection of prostatic cancer by radioimmunoassa A review. Hum. Pat hot. 9,618-620(1978). 2. Gittes, R., Acid phosphatase reappraised. N. Engi. J. Med. 297, 1398-1399(1977).
1.1 1.9
