Characterization of the enzymatic activity of PSM: comparison with brain NAALADase.

BACKGROUND: The prostate cancer marker prostate-specific membrane antigen (PSM) is highly homologous to the brain enzyme N-acetylated alpha-linked acidic dipeptidase (NAALADase). NAALADase is known to cleave terminal carboxy glutamates from both the neuronal peptide N-acetylaspartylglutamate (NAAG) and folate polyglutamate. In this report, we compare the NAAG hydrolyzing activity of NAALADase and the prostate enzyme PSM. METHODS: Using a NAAG hydrolytic radioenzymatic assay, we compared the pharmacological and kinetic properties of the brain and prostate enzymes. RESULTS: Eight normal prostate tissues from different species exhibited NAAG hydrolyzing activity. Among 14 cancer cell lines examined, activity was observed in human LNCaP, PC-82, and rat Dunning G and AT-1 cells. Brain exhibited membrane-localized activity exclusively, while the prostate enzyme had activity in both membrane and cytosolic fractions. The only observed pharmacological difference was the sensitivity to their putative substrates, folate polyglutamate and NAAG. Kinetically, the soluble form of the prostate enzyme had two catalytic sites, while the membrane-bound form exhibited single site kinetics with a lower Vmax than the brain enzyme, which may suggest a less active hydrolase in the prostate. CONCLUSIONS: The brain enzyme NAALADase and the prostate enzyme PSM are remarkably similar. The importance of the differences in substrate specificities and kinetic parameters remains to be elucidated.

Ejaculatory abnormalities in mice with targeted disruption of the gene for heme oxygenase-2.

Nitric oxide (NO) is well established as a neurotransmitter in the central and peripheral nervous systems. More recently, another gas, carbon monoxide (CO) has also been implicated in neurotransmission. In the nervous system CO is formed by a subtype of heme oxygenase (HO) designated HO2. HO2 is localized to discrete neuronal populations in the brain resembling localizations of soluble guanylyl cyclase, which is activated by CO. CO may also function in the peripheral autonomic nervous system, in conjunction with NO. The majority of ganglia in the myenteric plexus possess both HO2 and neuronal NO synthase (NOS). Defects in myenteric plexus neurotransmission occur both in mice with targeted deletion of genes for HO2 and neuronal NOS. HO2 also occurs in other autonomic ganglia including the petrosal, superior cervical and nodose ganglia. Neuronal NOS is localized to neurons regulating male reproductive behavior, such as penile erection, and NOS inhibitors prevent erection. Because of the other parallels between NO and CO, we speculated that CO may play a role in male reproductive behavior. In the present study we describe HO2 localization in neuronal structures regulating copulatory reflexes. Reflex activity of the bulbospongiosus muscle, which mediates ejaculation and ejaculatory behavior, is markedly diminished in mice with targeted deletion of the gene for HO2 (HO2-).

Immunohistochemical description of nitric oxide synthase isoforms in human clitoris.

PURPOSE: Our aim was to identify and localize nitric oxide synthase isoforms in the human clitoris in support of the hypothesis that nitric oxide mediates erectile function in this organ. MATERIALS AND METHODS: Nitric oxide synthase immunohistochemistry studies specific for neuronal, inducible and endothelial isoforms of the enzyme were performed on human clitoral tissue obtained from 4 patients (3 with female pseudohermaphroditism and 1 with true hermaphroditism) at feminizing genitoplasty and from 1 phenotypically normal woman at autopsy. RESULTS: Neuronal nitric oxide synthase immunoreactivity was detected in nerve bundles and fibers coursing within the glans clitoris and corpora cavernosa of the clitoris, predominating in the latter tissue. Specific inducible nitric oxide synthase immunoreactivity was not identified. Endothelial nitric oxide synthase immunoreactivity was detected in vascular and sinusoidal endothelium of these tissues with a predominance in the glans clitoris. CONCLUSIONS: The presence and anatomical localizations of nitric oxide synthase isoforms in the human clitoris indicate that nitric oxide is generated in this organ. These data suggest that nitric oxide may be involved in the erectile physiology of the clitoris as a modulator of clitoral smooth muscle activity. Functional studies are required to support this hypothesis.

Urinary bladder-urethral sphincter dysfunction in mice with targeted disruption of neuronal nitric oxide synthase models idiopathic voiding disorders in humans.

Idiopathic voiding disorders affect up to 10-15% of men and women. We describe bladder abnormalities in mice with targeted deletion of the gene for neuronal nitric oxide synthase which model the clinical disorders. The mice possess hypertrophic dilated bladders and dysfunctional urinary outlets which do not relax in response to electrical field stimulation or L-arginine. The mice also display increased urinary frequency.

Nitric oxide-dependent penile erection in mice lacking neuronal nitric oxide synthase.

BACKGROUND: Nitric oxide (NO) has been implicated as a mediator of penile erection, because the neuronal isoform of NO synthase (NOS) is localized to the penile innervation and NOS inhibitors selectively block erections. NO can also be formed by two other NOS isoforms derived from distinct genes, inducible NOS (iNOS) and endothelial NOS (eNOS). To clarify the source of NO in penile function, we have examined mice with targeted deletion of the nNOS gene (nNOS- mice). MATERIALS AND METHODS: Mating behavior, electrophysiologically induced penile erection, isolated erectile tissue isometric tension, and eNOS localization by immunohistochemistry and Western blot were performed on nNOS- mice and wild-type controls. RESULTS: Both intact animal penile erections and isolated erectile tissue function are maintained in nNOS mice, in agreement with demonstrated normal sexual behaviors, but is stereospecifically blocked by the NOS inhibitor, L-nitroarginine methyl ester (L-NAME). eNOS is abundantly present in endothelium of penile vasculature and sinusoidal endothelium within the corpora cavemosa, with levels that are significantly higher in nNOS- mice than in wild-type controls. CONCLUSIONS: eNOS mediates NO-dependent penile erection in nNOS- animals and normal penile erection. These data clarify the role of nitric oxide in penile erection and may have implications for therapeutic agents with selective effects on NOS isoforms.