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AMP-activated protein kinase (AMPK) is tightly regu-Mammalian AMP-activated protein kinase (AMPK) 1 plays a key role in the regulation of energy homeostasis and is highly conserved among animals, plants, and fungi (reviewed in Refs.

Mannan-binding lectin (MBL)-associated plasma protein (MAp19) is an alternatively spliced form of MBLassociated serine protease-2, a component of a complement activation cascade. We observed that MAp19 is excreted in human urine. Interestingly, the amount of MAp19 was higher in urine of renal cell carcinoma patients than healthy people. Pretreatment of urine dialysate with 50 mM EDTA increased the recovery of MAp19, suggesting that MAp19 is a calcium-binding protein. The recombinant MAp19 showed a strong inhibition of calcium oxalate crystal growth in vitro in a concentrationdependent manner. Thus, we conclude that MAp19 plays a role in the inhibition of calcium oxalate renal stone formation.z 1999 Federation of European Biochemical Societies.

Phosphatidylinositol (PI) 3-kinase plays an important role in transducing the signals of various growth factor receptors. However, the regulatory mechanism of PI3-kinase activity by these growth factor receptors is not completely understood. Therefore, we attempted to clarify the regulatory mechanism of PI3-kinase using insulin and 3T3 L1 fibroblasts. Our results showed that insulin stimulated PI3-kinase activity seven-fold and concomitantly phosphorylated a p85 subunit at the tyrosine residue. However, this tyrosine phosphorylation was not significant in the activation of PI3-kinase as the PI3-kinase pulled down by the overexpressed GSTp85 fusion protein showed as high an activity as the immunoprecipitated one. The p 110 subunit was phosphorylated at both serine and tyrosine residues without insulin treatment. Since the p h o s p h o r y l a t i o n state was not changed by insulin. The r e s u l t s suggested that phosphorylation of the p110 subunit does not control PI3-kinase activity. Finally, it was shown that the insulin receptor substrate-1 (IRS-1) binding to PI3-kinase was not sufficient for full activation because the amount of IRS-1 pulled down by the GST-p85 fusion protein reached almost maximum, after incubation with insulin-treated cell lysates for 20 min, whereas PI3-kinase activity reached its maximum only after incubation for 5 h. All results suggest that the phosphorylation of p85 subunit at tyrosine residues and phosphorylation of p 110 subunit at tyrosine or serine residues are not functionally significant in the regulation of PI3-kinase activity. They also suggest that PI3-kinase is needed to bind to other protein(s) as well as the insulin receptor substrate-1 for full activation.

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