Identification of Heat Stable Proteins in the Fatty Livers of Thyroidectomized Chickens

Abstract

Marked growth retardation has been well documented in thyroidectomized chickens. However, in these chickens, fatty liver and enlarged deposits of abdominal fatty tissue are also induced. The aim of the present study was to identify proteins that induce the fatty livers of thyroidectomized chickens. Heat stable proteins were selected for ease of analysis. Four protein bands were detected by SDS-PAGE with CBB staining after incubation at 70°C for 10min. The degree of CBB staining suggested that the expression of the 25-, 40- and 45-kDa proteins increased, whereas that of the 35-kDa protein decreased, in the fatty livers of thyroidectomized chickens. Partial N-terminal amino acid sequences were determined from the random peptides of these four proteins. Partial amino acid sequencing suggested that the 35-kDa protein was the lactate dehydrogenase B (LDHB, EC 1.1.1.27) subunit, which is primarily composed of LDH-1 isozyme, although this subunit is not abundant in mammal livers. Further analysis revealed that this 35-kDa protein acts as a dehydrogenase, with lactic acid as the substrate. It was thus identified as the LDHB subunit. The 40-kDa protein was identified as alcohol dehydrogenase 1 (ADH1, EC 1.1.1.1), and the 45-kDa protein as betaine homocysteine methyltransferase (BHMT, EC 2.1.1.5), an enzyme in the homocysteine cycle. The 25-kDa protein appeared to be a novel protein. These findings suggest that the metabolic pathway from pyruvic acid to ethanol is accelerated in the fatty livers of thyroidectomized chickens.