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Hexokinase (ADP: D‐hexose‐6‐phosphotransferase, EC 2.7.1.1) was studied in human thyroid carcinomas (n = 11), follicular adenomas (n = 32), and normal thyroid tissue (n = 21). The specific activity was significantly increased in carcinoma (0.163 ± 0.083 U/mg protein) compared with normal tissue (0.030 ± 0.010 U/mg protein) (P < 0.001). Specific activities of follicular adenomas are rather heterogeneous, but when subdivided into three groups according to histopathologic criteria, a significant difference was found between follicular adenomas group I and II and follicular adenomas group III. A lesser cellular differentiation of adenomas is indicated by the lower degree or even absence of colloid production and follicle formation. A higher proliferation rate may be assumed on the grounds of the irregularities in outline, the often defective pseudocapsule, and signs of compression of the surrounding tissue. The highest specific activity in adenomas was found in the group with the highest proliferative activity, i.e., group III, whereas the lowest specific activities were found in adenomas with the lowest grade of proliferation, i.e., group I; the former was comparable with values found in carcinomas and the latter was comparable with values found in normal thyroid tissue. An interesting difference was found when the compartmentation of hexokinase was compared in carcinomas of different degree of differentiation. In papillary carcinomas a significantly lower proportion of hexokinase (HK) is present in the cytosol in comparison to follicular and undifferentiated carcinomas. In carcinomas more HK II and less HK I was found in comparison with normal thyroid tissue. In contrast hexokinase isozyme composition and compartmentation in adenomas were not different from normal thyroid tissue.

Pyruvate kinase from anaplastic medullary thyroid carcinomas contains predominantly K-type subunits, whereas pyruvate kinase from differentiated medullary thyroid carcinomas consist of M-and K-type subunits in about equal proportion. In order to analyse the incorporation of phosphate in the respective isozymes after endogenous phosphorylation of cytosolic extracts with [a2P]ATP, homotetrameric isozymes as well as heterotetrameric hybrids of differentiated tumors were resolved by affinity chromatography on Blue-Sepharose CL-6B and, if necessary, further purified by immunoprecipitation. SDS-polyacrylamide gel electrophoresis of purified isozymes and subsequent autoradiography showed the incorporation of phosphate in the K4-type isozymes, but not in the other isozymes. The phosphorylation appeared to be cAMP-independent and occurred on a serine residue.

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