2D-PAGE ANALYSIS - ADRENERGICALLY REGULATED PINEAL PROTEIN AIP-37 6 IS A PHOSPHORYLATED ISOFORM OF CYTOSOLIC MALATE-DEHYDROGENASE/

The adrenergic transmitter norepinephrine (NE) dramatically increases the prominence of only two out of the hundreds of [S-35]methionine-lab eled pineal proteins resolved by two-dimensional polyacrylamide gel el ectrophoresis (2D-PAGE). One of these regulated proteins is AIP 37/6 ( 37 kDa, pI similar to 6). The labeling of this protein is increased si milar to 100-fold by NE. In the study presented here the identity of A IP 37/6 was investigated. The results of microsequencing, immunochemic al analysis of 2D-PAGE blots and size exclusion chromatography indicat e that AIP 37/6 is an isoform of cytosolic malate dehydrogenase (cMDH; similar to 36.3 kDa; pI similar to 6.5). Associated studies indicate that this isoform is phosphorylated whereas the bulk of cMDH is not. C otranslational phosphorylation of cMDH is discussed.