PubMed · 3898788
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M R Rahmani. 1985. Tumefactive biliary sludge.. https://doi.org/10.2214/ajr.145.4.860
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As shown by circular dichroism spectroscopy, biliverdin preferentially adopts an M-helicity conformation on human serum albumin in aqueous buffer, pH 7.5, whereas biliverdin exhibits only a weak preference for the P-helicity conformation on bovine serum albumin at the same pH. Upon rapid reduction of the complexes with sodium borohydride, P-helicity bilirubin-IX alpha is obtained on the human albumin complex, and M-helicity bilirubin-IX alpha is obtained on the bovine serum albumin complex. Thus, biliverdin in effect undergoes an inversion of chirality upon reduction. Since the reduction did not afford a rubin with the same helicity as that of the verdin, the observations point to a hitherto undetected conformational mobility of albumin-bound bilirubin.
It was the purpose of the present study to investigate whether the decrease in the ability of plasma albumin to bind bilirubin, noted in pregnancy and during delivery, takes place in one step, during pregnancy alone, or in two steps, during both pregnancy and delivery. Furthermore, it was investigated whether a possible decrease during labor was related to the method of delivery itself. The material comprised (a) 17 pregnant women who delivered vaginally; (b) 25 women who were delivered by Cesarean Section; and (c) a group of 25 non-pregnant women. The reserve albumin concentration for binding of MADDS (a measure of the binding of unconjugated bilirubin), the total albumin concentration and the ratio between them were constant in the 6-week period up to birth and were significantly lower than the corresponding values in the non-pregnant group. During labor a significant decrease in reserve albumin and ratio of reserve albumin to total albumin was observed, while no change in the total albumin concentration was noted. No significant difference in reserve albumin concentration, total albumin concentration and ratio between them was found when the group of mothers who delivered vaginally was compared to the Cesarean Section group. It is concluded that the decrease in the ability of plasma albumin to bind unconjugated bilirubin takes place stepwise. The first step is a significant reduction during pregnancy followed by a further decrease during labor. The method of delivery is of no significance.
Coproporphyrinogen III oxidase activity in human lymphocytes was found to be inhibited by cadmium and mercury but not by lead. The organo-metal compounds tributyltin and methylmercury were effective inhibitors of this haem biosynthetic pathway enzyme. Haemin (the ultimate product of the pathway) and bilirubin (a product of haem catabolism) were also shown to be inhibitory. Kinetic studies performed under initial velocity conditions showed that bilirubin was a non-competitive inhibitor and that one bilirubin molecule was bound to both the enzyme and enzyme substrate complex. The analysis also showed haemin to be a non-competitive inhibitor in which two haemin molecules bind to the enzyme whereas the enzyme substrate complex accepts only one haemin molecule. The possible physiological significance of the inhibition of coproporphyrinogen III oxidase activity by haemin and bilirubin is discussed.