NMR studies of 1H resonances in the 10-18-ppm range for cytosolic aspartate aminotransferase

Continuing a previous investigation (Kintanar, A., Metzler, C. M., Metzler, D. E., and Scott, R. D. (1991) J. Biol. Chem. 266, 17222-17229), we have recorded 1H NMR spectra at 500 MHz in the 10-18-ppm range for the 93-kDa porcine cytosolic aspartate aminotransferase and for four specific mutant forms of the enzyme in which histidine 68 has been replaced by lysine or histidine 143, 189, or 193 has been replaced by glutamine. We have correlated resonances for apoenzyme, pyridoxamine and pyridoxal phosphate forms, and dicarboxylate complexes and have assigned imidazole NH resonances of active site histidines. The chemical shifts of several resonances undergo pH-dependent changes around the pKa of the Schiff base proton at the active site. Other resonances shift upon binding of dicarboxylates or other ligands. Phosphate or carboxylate ions, which can also occupy the site of the substrate's alpha-carboxylate, cause rapid exchange of the Schiff base proton. Although most resonances in the 10-18-ppm range disappear rapidly in D2O, a few are retained for months in the presence of the dicarboxylate inhibitor glutarate. We demonstrate that changes in chemical shifts and in exchange rates are sensitive indicators of electronic interactions of the enzyme with ligands and of conformational change. Nuclear Overhauser effects from NH protons have allowed us to identify resonances of CH protons of the imidazole rings of histidines 143, 189, and 193. Observed and predicted chemical shifts have been compared. We conclude that the net charge on this histidine cluster is zero but that some negative charge from the aspartate 222 carboxylate is donated inductively into the histidine 143 ring. Studies of the related enzyme from Escherichia coli are provided in an accompanying paper (Metzler, D. E., Metzler, C. M., Scott, R. D., Mollova, E. T., Kagamiyama, H., Yano, T., Kuramitsu, S., Hayashi, H., Hirotsu, K., and Miyahara, I. (1994) J. Biol. Chem. 269, 28027-28033). Our approach should be applicable to the study of active sites of a broad range of relatively large proteins.

Cerebellar porencephaly in an adult--case report

A 51-year-old female presented with an extremely unusual cerebellar porencephalic lesion manifesting as progressive cerebellar signs and cranial nerve pareses. T1-weighted magnetic resonance imaging demonstrated a low-signal-intensity area in the left cerebellar hemisphere suggesting a cavity communicating with the fourth ventricle. Histological study showed the wall of the cavity contained nonspecific gliosis. A diagnosis of porencephaly was made.

Sequential changes in ischemic edema following transient focal cerebral ischemia in rats: magnetic resonance imaging study

Sequential and regional changes in ischemic edema following various durations of focal cerebral ischemia were studied by magnetic resonance (MR) imaging in a rat unilateral intraluminal middle cerebral artery occlusion model. Occlusion was performed from 5 minutes to 5 hours. T2-weighted images were obtained chronologically 6 hours after onset of ischemia, on day 1 and day 7. An immunohistochemical study using antibodies to calcineurin and glial fibrillary acidic protein was performed to observe histological changes in the ischemic brain. The T2 high-signal-intensity areas representing ischemic edema were observed in the lateral striatum and/or the cerebral cortex by day 1 in all rats with 1- to 5-hour ischemia, and the areas were larger and detected earlier with longer durations of ischemia. In three of six rats with 15-minute ischemia and five of six rats with 30-minute ischemia, the T2 high-signal-intensity areas appeared transiently on day 1 in the dorsolateral striatum where loss of neurons expressing calcineurin immunoreactivity and associated gliosis were found. MR imaging in animal models of reversible focal ischemia can achieve sequential and noninvasive evaluation of dynamic regional changes in ischemic edema.

Subdivisional ischemic injury of the unilateral striatum causes apomorphine-induced rotational behavior in rats

Behavioral and histological studies were performed on a reversible ischemia model in rats. At 60 days after unilateral transient middle cerebral artery occlusion for 30 min, the operated rats exhibited the ipsiversive rotational behavior elicited by systemic administration of dopamine receptor agonist apomorphine in a dose-dependent manner. Histologically, the ipsilateral striatum of the rats showed a subdivisional ischemic injury, while the nigral dopaminergic neurons appeared intact. The striatal lesions having a cell type-specific injury were located in the dorsolateral portion of the rostral striatum and in the lateral portion of the caudal part of the nucleus. Thus, the transient cerebral ischemia could successfully produce selective damage of a striatal subdivision, which causes an abnormality in motor controls in response to dopamine receptor stimulation. The present data may provide a part of functional and anatomical basis for understanding the movement disorders associated with basal ganglia dysfunction (e.g., parkinsonism), which may occur in patients with cerebrovascular disorders.