We examined thyroidectomized chickens in terms of plasma lipid concentration and protein expression within the liver. Although the body weight of thyroidectomized chickens was remarkably low due to growth retardation, the livers were enlarged and fatty compared to those of sham-operated chickens. An increase in phospholipid, triglyceride, and total cholesterol levels within the blood plasma of thyroidectomized chickens was observed, clearly reflecting increased lipid synthesis within the liver. Overexpression of some proteins, for example, 29- and 45-kDa proteins, was observed in thyroidectomized chicken livers by means of electrophoresis. A peptide map was made for the protein that exhibited the greatest degree of overexpression. One of them demonstrated a molecular mass of 45 kDa and an isoelectric point (pI) between 7.5 and 8.0, depending on its form. Partial N-terminal amino acid sequences were determined from three random peptides of this protein. The amino acid sequence of this protein showed a high degree of homology with the betaine-homocysteine S-methyltransferase (BHMT, EC 2.1.1.5) of some mammalian species. We identified this protein as chicken BHMT because, in addition to its sequence homology with mammalian BHMT, there were similarities were also observed between this 45-kDa protein and mammalian BHMT with respect to molecular mass and isoelectric behavior. In the liver, 10 d after thyroidectomy, the synthesis of hepatic BHMT had already been enhanced, and the high expression was maintained at 50 d of age. Generally, BHMT catalyzes the transfer of a methyl group from betaine to L-homocysteine. In addition, it seems that this enzyme is also closely related to lipid metabolism in the liver; in this study expression of BHMT in the liver corresponded to plasma lipid levels. Moreover, hypothyroidism may be directly or indirectly related to overexpression of BHMT. Due to similarities between the BHMT of chickens and mammalian species, the chicken model might provide a useful means by which to study BHMT, its role in lipid metabolism, and methods of targeting the expression of BHMT. Another 29-kDa protein was unidentified in the homology search.
This study was conducted to elucidate the effects of dietary phytic acid supplementation on organs and serum components in broiler chickens. A total of 30 1-day-old broiler chicks were divided into three treatment groups (n= 10, each). The control group was fed normal diet and the other groups were fed diet supplemented with 0.06% and 0.12% phytic acid for 30 days. No differences in body and muscle weights and 21 serum biochemical parameters were detected between phytic acid treatments and the control. However, abdominal fat weight decreased significantly with 0.12% phytic acid treatment (P<0.05). Liver weight and certain serum lipid parameters changed slightly, although differences were not statistically significant. In addition, the correlation coefficient between abdominal fat and liver weights was 0.69 (P<0.05) in the control group, whereas no significant differences were observed in the phytic acid fed groups. It is possible that phytic acid may affect lipid metabolism in liver and/or abdominal adipose.
An NAD(P)H-dependent carbonyl reductase specifically expressed in thyroidectomized chicken fatty liver was crystallized using the sitting-drop vapour-diffusion method with polyethylene glycol 300 as the precipitant. The crystals belonged to the monoclinic space group C2, with unit-cell parameters a=104.26, b=81.32, c=77.27 Å, β=119.43°, and diffracted to 1.86 Å resolution on beamline NE3A at the Photon Factory. The overall Rmerge was 5.4% and the data completeness was 99.4%.
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 1*ῌ for +* min. The degree of CBB staining suggested that the expression of the ,/-, .*-and ./-kDa proteins increased, whereas that of the -/-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 -/-kDa protein was the lactate dehydrogenase B (LDHB, EC +.+.+.,1) subunit, which is primarily composed of LDH-+ isozyme, although this subunit is not abundant in mammal livers. Further analysis revealed that this -/-kDa protein acts as a dehydrogenase, with lactic acid as the substrate. It was thus identified as the LDHB subunit. The .*-kDa protein was identified as alcohol dehydrogenase + (ADH+, EC +.+.+.+), and the ./-kDa protein as betaine homocysteine methyltransferase (BHMT, EC ,.+.+./), an enzyme in the homocysteine cycle. The ,/-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.
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