The function of KCNAB1 (potassium voltage-gated channel subfamily A regulatory beta subunit 1, Ensembl gene identifier ENSG00000169282) is as follows. Regulatory subunit of the voltage-gated potassium (Kv) Shaker channels composed of pore-forming and potassium-conducting alpha subunits and of regulatory beta subunits (PubMed:17156368, PubMed:17540341, PubMed:19713757, PubMed:7499366, PubMed:7603988). The beta-1/KCNAB1 cytoplasmic subunit mediates closure of delayed rectifier potassium channels by physically obstructing the pore via its N- terminal domain and increases the speed of channel closure for other family members (PubMed:9763623). Promotes the inactivation of Kv1.1/KCNA1, Kv1.2/KCNA2, Kv1.4/KCNA4, Kv1.5/KCNA5 and Kv1.6/KCNA6 alpha subunit-containing channels (PubMed:12077175, PubMed:12130714, PubMed:15361858, PubMed:17156368, PubMed:17540341, PubMed:19713757, PubMed:7499366, PubMed:7603988, PubMed:7649300, PubMed:7890764, PubMed:9763623). Displays nicotinamide adenine dinucleotide phosphate (NADPH)-dependent aldoketoreductase activity by catalyzing the NADPH- dependent reduction of a variety of endogenous aldehydes and ketones (By similarity). The binding of NADPH is required for efficient down- regulation of potassium channel activity (PubMed:17540341). Oxidation of the bound NADPH restrains N-terminal domain from blocking the channel, thereby decreasing N-type inactivation of potassium channel activity (By similarity). {ECO:0000250|UniProtKB:P63144, ECO:0000269|PubMed:12077175, ECO:0000269|PubMed:12130714, ECO:0000269|PubMed:15361858, ECO:0000269|PubMed:17156368, ECO:0000269|PubMed:17540341, ECO:0000269|PubMed:19713757, ECO:0000269|PubMed:7499366, ECO:0000269|PubMed:7603988, ECO:0000269|PubMed:7649300, ECO:0000269|PubMed:7890764, ECO:0000269|PubMed:9763623}. [Isoform KvB1.2]: Isoform KvB1.2 shows no effect on KCNA1, KCNA2 or KCNB1. {ECO:0000269|PubMed:7890032, ECO:0000269|PubMed:7890764}.