Conversion of 5-aminolaevulinate into haem by liver homogenates. Comparison of rat and chick embryo

Publisher Website
Google Scholar
Abstract
The kinetics of the conversion of 5-aminolevulinate into heme and heme precursors was studied in homogenates of livers of rats and chick embryos. Homogenates of fresh liver from both species efficiently convert 5-aminolevulinate into heme. After frozen storage for 1 yr, homogenates of rat, but not chick, liver have decreased rates of formation of heme with accumulation of more protoporphyrin. The rate of heme formation after storage is restored by addition of Fe2+ and menadione. At all initial concentrations of 5-aminolevulinate tested (2 .mu.M-1 mM), homogenates of rat liver accumulate less protoporphyrin than heme. Homogenates of chick embryo liver accumulate more protoporphyrin than heme at concentrations of 5-aminolevulinate > 10 .mu.M. Conversion of protoporphyrin into heme by homogenates of fresh or frozen chick embryo liver is not increased by addition of Fe2+. Homogenates of liver from both species accumulate porphobilinogen; the kinetic parameters for this process reflect those of 5-aminolevulinate dehydratase. The rate-limiting enzyme for the hepatic conversion of 5-aminolevulinate into protoporphyrin is porphobilinogen deaminase. Chick liver, compared with rat liver, has only about 1/5th the activity of ferrochelatase, the final enzyme of the heme biosynthetic pathway, which inserts Fe2+ into protoporphyrin to form heme. Comparison of these results with previous studies indicates that the homogenate system described provides physiologically and clinically relevant information for study of hepatic heme synthesis and its control.

This publication has 26 references indexed in Scilit: