EFFECT OF TUNICAMYCIN ON APPEARANCE OF CARBOHYDRATE VARIANTS OF PLASMINOGEN IN RAT AND RABBIT PLASMA

The in vivo incorporation of [4,5-3H]leucine and [2-3H]mannose into the lysine-Sepharose affinity chromatography-resolvable carbohydrate variants of rat and rabbit plasminogen were studied in the absence and presence of tunicamycin (TM). When rabbits and rats were exposed to 0.5 mg TM/kg body wt for 30 min and 2 h, respectively, followed by a single pulse of [4,5-3H]leucine for 2 h, no radiolabel was found in rat or rabbit variant 1 plasminogen, whereas [4,5-3H]leucine was incorporated into variant 2 plasminogen. In similar experiments utilizing [2-3H]mannose in place of [4,5-3H]leucine, very little [2-3H]mannose was incorporated into either plasminogen variant in the presence of TM. The trichloroacetic acid-precipitable protein of rabbit plasma incorporated virtually identical quantities of [4,5-3H]leucine in the absence or presence of TM, under the above dosage regimens, while, at the same time, a large decrease in the incorporation of [2-3H]mannose was observed in the plasma proteins of rabbits treated with TM. Many of the plasma proteins may be secreted into plasma divested of asparagine-linked carbohydrate side chains. The functional difference (antifibrinolytic amino acid binding capacity) between the 2 plasma variants of plasminogen more than likely results from additional glycosylation of asparagine in variant 1 plasminogen that normally does not occur in variant 2 plasminogen.