Pyruvate kinase in normal human thyroid tissue and thyroid neoplasms

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Abstract
Pyruvate kinase (ATP: pyruvate-2-O-phosphotransferase, EC 2.7.1.40) was studied in human thyroid carcinomas (n = 9), follicular adenomas (n = 32), and normal thyroid tissue (n = 12). The specific activity in carcinomas (mean 0.94 ± 0.44) is significantly increased (P < 0.0001) in comparison with pyruvate kinase in normal tissue (mean, 0.14 ± 0.05). Specific activities of follicular adenomas are rather heterogeneous. When these tumors were divided into three groups of increasing proliferative activity as judged by histopathologic criteria, highest specific activities of pyruvate kinase were found in the group with the highest proliferative activity. On the other hand, specific enzyme activities of the least active tissues (colloid-containing follicular adenomas) were comparable to normal. The isoenzyme composition of normal thyroid tissue is characterized by the presence of K4, K3M, and K2M2 types of pyruvate kinase. In carcinomas, mainly K4, and K3M are found. Undifferentiated tumors express more K4 type compared with follicular and papillary carcinomas. Follicular adenomas with high specific activity show the same electrophoretic pattern as found in follicular carcinomas. Pyruvate kinase from malignant tumors is more inhibited by the amino acid L-alanine than the enzyme from normal thyroid tissue as a consequence of the presence of more K subunits in the malignant tissues. The K4 type from normal thyroid tissue is not kinetically different from the K4 type of carcinomas.

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