Zur Bestimmung der spezifischen Histidindecarboxylase

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Abstract
The decrease in histamine formation 10 min. after the addition of thyroid extracts is caused by the following factors: the consumption of histamine by diamine oxidase and histamine methyltransferase (largely inhibited by aminoguanidine and chlorpromazine) the formation of a complex between histidine and pyridoxal phosphate; the instability of the enzyme (decreased by glutathione); incubation under N2 (avoided by using O2). Optimal conditions for determination of specific histidine decarboxylase of thyroid glands are: 6.25x10-4 M aminoguanidine, 1x10-3 M chlorpromazine, 10-2 M glutathione and substrate saturation (10-2 M histidine). Under these conditions about 12,7 pmoles histamine/ mg protein and min., i.e. 27 [mu]g histamine/100 mg prptein and 3 h were formed, respectively. 1x103 M aminoguanidine and 5x10-3 M chlorpromazine inhibit the specific histidine decarboxylase by 90%. The importance of these results for the detection and determination of the specific histidine decarboxylase of various organs, and the sensitivity and specifity of fluorometric and isotopic methods are discussed.