Alkaline phosphatase is an ectoenzyme that acts on micromolar concentrations of natural substrates at physiologic pH in human osteosarcoma (SAOS-2) cells.

Alkaline phosphatase (ALP) was examined in cultured human osteosarcoma cells (SAOS-2) with respect to isoenzyme form, kinetic properties toward two natural substrates, and topography and nature of attachment to the plasma membrane. ALP in SAOS-2 homogenates is the tissue-nonspecific (TNS) isoenzyme and a phosphoethanolamine (PEA) and pyridoxal 5'-phosphate (PLP) phosphatase, as demonstrated by heat and inhibition profiles and electrophoretic mobility. Kinetic studies indicate that TNSALP in SAOS-2 cells has both a low- and a high-affinity activity. The high-affinity activity (showing the greater catalytic efficiency) is active at physiologic pH toward physiologic concentrations (microM) of PEA and PLP. TNSALP was shown to be an ectoenzyme in SAOS-2 cells by our findings in intact cell suspensions, where (i) PEA and PLP degradation in the medium nearly equaled that of whole cell homogenates, (ii) greater than 85% of ALP activity was inactivated by acid treatment, and (iii) ALP activity was quantitatively released by phosphatidylinositol-specific phospholipase C. Our findings indicate that, in SAOS-2 cells, TNS (bone) ALP functions as an ectoenzyme to degrade physiologic concentrations of extracellular natural substrates at physiologic pH.

Changes in epidermal forward scattering absorption after UVA or UVA-UVB irradiation.

Groups of skh-1 (albino) and Skh-2 (pigmented) hairless mice were irradiated for 125 hr using a modified GE F8T5-BL black light with and without a 3-mm plate glass filter to remove light below 320 nm. The epidermis was examined by forward scattering and by histological section postirradiation at 48 hr, 96 hr, 9 days, and 23 days. Changes in the epidermis of all animals were compared to control groups. Although no differences were seen between Skh-1 and Skh-2 mice, both the magnitude and shape of the forward scattering absorption curves were changed by the irradiation used. In both strains, differences which were detected at 48 hr postirradiation had returned to normal visually by 23 days, with no augmented pigmentation occurring in Skh-2 animals. At 23 days postirradiation, however, residual optical alterations were observed. This phenomenon, detected optically, may be skin acclimatization.