英语翻译
The activity of the microsomal system as a function of [Pi] is shown in fig.2.The response is very complex >70% of the microsomal activity is inhibited at -5 mM.An increase in activity between 0.1-l mM was consistently observed.The steepest slope of this phosphate inhibition curve occurred overa [Pi] range which is roughly that reported in muscle in situ [ 141.
A change in activity of from 70 - 30% of the maximal rate occurred over -3-8 mM phosphate.Thus,insitu the content of free phosphate may be an important modifying factor in muscle tissue and the rate of hydrolysis of phosphate compounds in fish muscle after death may play an important role in the rate at which trimethylamine oxide is degraded.
The effect of several other compounds which were shown to be activators or inhibitors of DMA production by the microsomal system of red hake muscle are given in table 2.Phenazine methosulfate and methylene blue were the most potent activators of
the system.These are compounds which can participate in electron transfer reactions and methylene blue is frequently used in the assay for this enzyme to increased activity.Trimethylamine and choline have similar structures to the substrate trimethylamine oxide and could be functioning as competitive inhibitors.
EDTA and citrate could possibly inhibit by chelating the Fe2+ in the reaction medium,and the inhibitory effect of Cu2+ might indicate that sulfhydryl groups were involved in the enzyme.
Conversion of trimethylaime oxide to DMA by the red hake muscle microsomal fraction was examined in the frozen and unfrozen state (table 3).DMA production in samples at temperatures above freezing were assayed after 1 h whereas samples in the frozen state were assayed after 3 h.These values,however,were all calculated on the basis of DMA yield/h reaction.