Cofactors are essential components of numerous enzymes, therefore their characterization by structural, biophysical, and biochemical approaches is crucial for understanding the resulting catalytic and regulatory mechanisms. In this chapter, we present a case study of a recently discovered cofactor, the nickel-pincer nucleotide (NPN), by demonstrating how we identified and thoroughly characterized this unprecedented nickel-containing coenzyme that is tethered to lactase racemase from Lactiplantibacillus plantarum. In addition, we describe how the NPN cofactor is biosynthesized by a panel of proteins encoded in the lar operon and describe the properties of these novel enzymes. Comprehensive protocols for conducting functional and mechanistic studies of NPN-containing lactate racemase (LarA) and the carboxylase/hydrolase (LarB), sulfur transferase (LarE), and metal insertase (LarC) used for NPN biosynthesis are provided for potential applications towards characterizing enzymes in the same or homologous families.

UNASSIGNED: Takotsubo syndrome (TS) is defined as transient left ventricular dysfunction, which is often related to an emotional or physically stressful event. We describe a case of TS in a lady with pyruvate carboxylase deficiency (PCD). Pyruvate carboxylase deficiency is rare condition with the majority of those affected demonstrating signs of failure to thrive, recurrent seizures, and metabolic acidosis. To our knowledge, this is the first documented case of TS in an individual with PCD.
UNASSIGNED: This 28-year-old female presented to the emergency department after a tonic-clonic seizure. For 4 days prior to the presentation, she had been suffering from cough and pyrexia. On Day 2, she developed abdominal pain associated with tachycardia and hypotension, and an elevated troponin (791 ng/L). The echocardiogram showed a severely impaired left ventricular systolic function, regional wall motion abnormalities (RWMAs), and a visually estimated left ventricular ejection fraction of 25-30%. Eight days following admission her clinical state significantly improved, with a reduction troponin to 60 ng/L. A repeat echocardiogram on Day 9 showed complete resolution of cardiac function with no RWMAs. Following this, she was discharged from hospital the next day with a diagnosis of TS.
UNASSIGNED: This is the first case report of TS in a patient with PCD. In this case, multiple aetiologies of TS such as emotional and physical stress, seizures, and acute infection were considered. This case also highlights that TS should be an important differential diagnosis in patients presenting with cardiac symptoms.