AbstractThe enzymes of the leucine pathway ofCandida maltosawere investigated and the regulatory pattern was established. l‐leucine inhibited the α‐isopropylmalate (IPM) synthase, the first enzyme of the pathway. The inhibition was competitive with respect to α‐ketoisovalerate (Ki= 0.81 mm) and non‐competitive with respect to acetyl‐CoA. The Km values of the enzyme were estimated to be 0.57 mm for α‐ketoisovalerate and 0.064 mm for acetyl‐CoA. TheKmvalues of the second enzyme, IPM dehydratase, were estimated to be 4.57, 0.57 and 1.79 for α‐IPM, β‐IPM and citraconate, respectively. TheKmvalues of the β‐IPM dehydrogenase were calculated to be 0.42 mm for β‐IPM and 0.34 mm for NAD+. For this enzyme a novel regulatory pattern, its inhibition by l‐valine, was found. The inhibition was competitive with respect to β‐IPM (Ki= 1.7 mm) and non