Distribution of Alkylglycerone-Phosphate Synthase in Subcellular Fractions of Rat Liver

Abstract

Subcellular fractions of rat liver were isolated by density-gradient centrifugation on a linear Metrizamide gradient and were assayed for marker enzymes of peroxisomes, lysosomes, microsomes and mitochondria. Alkylglyceronephosphate synthase catalysing the formation of the ether bond in glycerolipids was also determined along the gradient. The enzyme was found to be enriched in the peroxisomal and the microsomal fractions thus, displaying a bimodal distribution pattern. Two reaction-products each, alkylglycerone phosphate and alkylglycerone were obtained in the enzymic assays performed, the ratio of which was clearly dependent upon the fraction employed. Alkylglycerone phosphate was mainly synthesized by the 'peroxisomal synthase', whereas an inverse proportion was observed assaying the microsomal counterpart. Furthermore, comparing the mean specific activities of both the enzymes the microsomal one was shown to be roughly twice as active in metabolizing 1-0-palmitoylglycerone 3-phosphate, simultaneously displaying a somewhat different sensitivity to NaF. These findings provide a first line of evidence, that two separate synthases, one in microsomes and another one in peroxisomes might be engaged in the biosynthesis of 1-0-alkylglycerolipids in rat liver. Subzelluläre Verteilung der AlkyIglyceronphosphat-Synthase in der RattenleberZusammenfassung: Mittels Dichtegradientenzentrifugation unter Verwendung linearer Metrizamid-Gradienten wurden aus Rattenleber subzelluläre Fraktionen gewonnen. Neben Leitenzymen für Peroxisomen, Lysosomen, Mikrosomen und Mitochondrien wurde in den einzelnen Gradientenfraktionen auch Alkylglyceronphosphat-Synthase bestimmt. Die Synthase katalysiert im Rahmen der Biosynthese von sogenannten Etherlipiden die Substitution eines langkettigen Acylrestes durch einen Fettalkohol.

Proteins and enzymes of the peroxisomal membrane in mammals

“…Although the product (acyI-DHAP) of the reaction catalyzed by DHAP-AT is transported very fast across the membrane and can diffuse to the endoplasmic reticulum, it is also utilized at a high efficiency as substrate by alkyl-DHAP synthase, suggesting a close interaction of the two enzymes in the peroxisomal membrane [115,116]. Indeed, aikyI-DHAP synthase has generally been found to be colocalized with DHAP-AT in peroxisome fractions on centrifugation [77,101,111,123,130,132,142,150,151]. As has been observed for DHAP-AT, lack of peroxisomes in some inherited diseases also leads to a deficiency in alkyI-DHAP synthase activity [135,[152][153][154][155].…”