Isozyme Variations in Human Cells Grown in Vitro: I. Amino Acid Naphthyl Amidase

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Abstract
Four different electrophoretic variants were observed in normal skin cells as well as in 5 heteroploid cell lines. Cultured normal skin shows regularly isozyme components not present in skin biopsies. The process of cultivation may have induced the synthesis of these enzymes. Five different heteroploid cell lines showed markedly lower enzyme activity than the normal diploid skin cells. The enzyme activity of He La cells increases with increasing amounts of human serum in the medium. One component of He La cells shows a marked response to serum alterations. This isozyme variant is activated by L-methionine, lacks sialic acid and is present in all human tissues examined except skin. Attempts to induce enzyme synthesis by means of chemically defined substrates gave negative re suits.